**9. Conclusions**

• repolarization is the result of opening K+

For unclear reasons, the amount of K+

130 Circadian Rhythm - Cellular and Molecular Mechanisms

*8.5.2. Calcium and acid-base balance*

the -COOH does not change to -COO<sup>−</sup>

and the calcium binds to -COO<sup>−</sup>

comes to membrane processes.

H+

tracellular K+

channels and the subsequent outward K+

concentration. In hyperkalemia, therefore, acceleration of repolarization occurs.

Electrolyte abnormalities are becoming an increasingly important cause of arrhythmias. In humans monitored using electrocardiography, spiky and narrow T-waves (acceleration of repolarization) are the most common manifestations, QRS complex enlargement and prolongation of the PQ interval (slow depolarization). If hyperkalemia deepens, atrial activity may disappear, and ventricles are stimulated from AV node with resulting bradycardia. In severe hyperkalemia, the QRS complex expands, with consequent risk for ventricular fibrillation and cardiac arrest.

Although electrocardiographic (ECG) changes in hyperkalemic rats are poorly understood, it is clear that excess plasma potassium may also alter cardiac excitation. In addition, the effects of hyperkalemia on ECG in rats may differ from other species that do not have ST segments and longer QT intervals. At testing, the effects of two local anesthetics (bupivacaine and lidocaine) at normocalcemia and hyperkalemia were found that hyperkalemia with concentration 9.0 mmol/l had little effect on heart rate or AV conduction in the absence of bupivacaine or lidocaine. Nevertheless, the effect of local anesthetics on slowing the ventricular rate was significantly enhanced. For bupivacaine, ventricular deceleration to 50% vs. control, during hyperkalemia, was performed almost completely through inhibition of AV conduction whereas for lidocaine through not only inhibition of AV conduction but also atrial rate. Regardless of the mechanism, hyperkalemia of this grade increased the ventricular slowing effect of bupivacaine and lidocaine [144]. Kuwahara et al. [145] described changes in rat ECG in dependence on K+ levels. In moderate hyperkalemia, an increased amplitude of T wave occurred. The duration of the PR interval and the QRS complex was slightly reduced, and the P wave disappeared in most rats at potassium levels above 8.0 mmol/l. In advanced hyperkalemia (plasma potassium concentration higher than 7.5 mmol/l), conduction was suppressed in all parts of the heart.

As for hypokalemia, except impacts on other functions and systems, heart failure and cardiac rhythm are typical of cardiac symptoms. On the ECG, low, flat, or inverted T-waves and prolongation of the QT interval can be seen. Supraventricular and ventricular extrasystoles occur episodically.

Similarly as the proton is exchanged for the potassium cation, a calcium cation is also exchanged for protons. Plasma proteins play a key role in this mechanism. Blood plasma proteins behave as buffers, primarily due to carboxyl groups and amino groups. As regard the carboxyl groups, these groups are in protonic, nondissociated state (-COOH) in the acidic environment. In the alkaline environment, they begin to buffer and their dissociation into the carboxylate -COO− occurs, which is able to bind very effective especially Ca2+. It means that in the case of acidosis,

It can also be said that the pH depends on what part of the calcium will be ionized and what part will be nonionized. The practical consequence is that alkalosis leads to ionized hypocalcemia, acidosis, on the contrary, to ionized hypercalcemia. Although total calcium does not change, we have to realize that ionized calcium is metabolically active, especially when it

.

, and in the case of alkalosis, it dissociates to -COO<sup>−</sup>

from the cell paradoxically increases with increasing ex-

current.

and

After summarizing the results from the analysis of acid-base balance parameters (**Table 6**), we concluded that there are differences in the final status of the rat internal environment that depend on the LD cycle and on the type of anesthesia.

In the light part of the day, under P anesthesia, the rats are in a state of acidosis, hypercapnia, and hypoxia, and elevated levels of bicarbonate have been reported. Similarly, it is also in the dark, but with mild acidosis, hypercapnia and hypoxia with a moderate decrease to normal pO2 values but with elevated levels of bicarbonate. Saturation of hemoglobin by oxygen was at the same level in both light parts of the rat regimen day, and at approximately 87%, the efficiency of the buffer system was not impaired because the values were within the normal range.

Under K/X anesthesia, we found a dependence on LD cycle in all monitored parameters. In the light part of the day, unambiguous acidosis, pCO2 ranging from normocapnia to hypercapnia, pO in the hypoxic range, relatively large range of bicarbonate (from reduced to increased levels) levels and lower saturation (around 85%) were observed. In the dark part of the day, from normal to alkaline pH, hypocapnia, moderate decreased to normal pO2 but with a reduced level of bicarbonate. Different values were in saturation of hemoglobin by oxygen, where higher saturation was during the dark (active) part (around 90%). The efficiency of the buffer system moved within the normal range in both light parts of the day.

Under Z anesthesia, the status was as follows: acidosis, hypercapnia, hypoxia to normoxia, and normal levels of bicarbonate in the light part of the day. In the dark part of the day, the state of the internal environment was from acidic to normal, hypercapnia, and pO2 moved from mild hypoxia to normoxia at a normal to moderately elevated level of bicarbonate. The saturation of hemoglobin by oxygen fluctuated around 89% in both light parts of the rat regimen day, and BB and BE were also in the normal range; thus, buffering capacity remained intact.

It was concluded that P anesthesia is not the most appropriate type of general anesthesia to use in chronobiological rat models. It is likely to produce a more acidic environment than K/X and Z anesthesias, and although an LD difference in P anesthesia was not recorded, the pH values were the lowest in both light parts of the rat regimen day compared with K/X and Z anesthesias. Initially, acidosis is induced, irrespective of the synchronization of animals with the LD cycle, and therefore, it is not possible to monitor periodic changes in the functions of individual systems that are primarily dependent on changes in extracellular pH. As a result, P probably and immediately reduces either the activity of the buffer systems or inhibits the regulatory mechanisms associated with the maintenance of isohydria, independently of the LD cycle. In this regard, K/X and Z anesthesias may be more appropriate for general anesthesia because the arterial pH varies within the range of isohydria. This assumption is only valid if the rat experiments are performed under K/X and Z anesthesia in the dark (i.e., active) parts of the day.

**Author details**

Address all correspondence to: pavol.svorc@upjs.sk

Department of Physiology, Medical Faculty Safarik's University, Kosice, Slovak

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Pavol Svorc

**References**

7613.106451

org/10.1007/BF03002209

Hypoxia modifies circadian oscillations of important variables, such as body temperature and metabolism, and may lead to the expectation that the rhythms of many functions are disrupted by hypoxia according to their relationships and association with the primary variables [146]. This effect appears to be apparent in rats under P anesthesia. From a chronobiological point of view, P anesthesia, therefore, is not a suitable form of general anesthesia. Using this type of anesthesia, with the exception of the initial hypoxia and hypercapnia, the LD differences in pO2 and pCO2 are eliminated. As a result, the effect of initial hypoxia and hypercapnia on the circadian rhythms of oxygen-dependent systems, immediately after administration of anesthetics, can significantly affect the end result.

Based on the results of this study, we concluded that general anesthesia affects the circadian fluctuation of arterial acid-base balance and plasma concentrations of some ions (**Table 9**). This should be taken into account, and experiments should start with a normal range of acidbase balance. Even at the beginning of the experiment, the altered internal environment may affect the activity of systems whose functions are primarily dependent on acid-base balance.


**Table 9.** Internal environment under general anesthesia dependent on the light-dark cycle in the rat.
