OLGA LARINA⁽¹⁾, Volodimir Manko^(2)
(1)DEPARTMENT OF HUMAN AND ANIMAL PHYSIOLOGY. I.FRANKO LVIV NATIONAL UNIVERSITY - LVIV . Ukraine
⁽²⁾Dept. Of Human and Animal Phisiology. I. Franko Lviv National University - Lviv. Ukraine

	[Endocrinology]	[Physiology]

RESULTS

Effect H⁺ on functioning of salivary gland secretory cell Na⁺-Ca²⁺ exchanger in Chironomus plumosus L. larva was investigated in conditions of simultaneous changes of intra- and extracellular pH level and its changes by turn.

acidification of extracellular solution from pH 7.2 to pH 5.0 evoked decrease of I_Na(Ca) amplitude from (3.72+/-0.43)*10^-10 A to (2.68+/-0.29)*10^-10 A, that is by (25.99+/-5.23)% (P<0.05, n=7) and according to preliminary studies (Klevets et al., 1996). The influence of intracellular solution acidification to pH_i 5.0 was compared in seven preparations. It was somewhat variable from preparation to preparation. In four cases we observed insignificant reduction of Na⁺-Ca²⁺ exchange current amplitude, and I_Na(Ca) amplitude didn’t change in three cases. Thus Na⁺-Ca²⁺ exchange current insignificantly reduced at average by (10.48+/-7.85)%. Statistically unauthentic decrease of Na⁺-Ca²⁺ exchange current amplitude was also evoked by simultaneous reduction of intra- and extracellular solution pH level.

Fig.1 shows the effect of alkalization on Na⁺-Ca²⁺ exchanger functioning. Increase of extracellular solution pH level from pH 7.2 to pH 9.0 led to increase of I_Na(Ca) amplitude (Fig.1) from (8.35+/-1.41)*10^-10 A to (11.03+/-1.83)*10^-10 A (i.e. by (32.02+/-6.13)% ; p<0.01, n=7). This change was reversible when physiological level of pH_e was restorated. Alkalization of intracellular solution evoked significant decrease of I_Na(Ca) amplitude by (66.70+/-7.05)% (p<0.01, n=7). I_Na(Ca) amplitude achieved (10.98+/-2.42)*10^-10 A after restoration of physiological pH_i level.

Simultaneous intra- and extracellular solution alkalization caused significant reduction of the amplitude of inward Na⁺-Ca²⁺ exchange current (by (77.65+/-6.82)%; p<0.01, n=7). Moreover, in two cases we registered reversible changes of current direction from inward to outward. The outward current amplitude was (6.88+/-2.06)*10^-10 A.

Gradual intracellular solution alkalization to pH 8.0, 8.5, 9.0 and 10.0 evoked I_Na(Ca) reduction by (4.03+/-5.15), (30.72+/-10.18), (59.96+/-12.21) and (74.17+/-10.69)%, respectively (see Fig. 1 B). Moreover, in two cases from six (at pH_i 9.0 and 10.0) we registered outward phase of I_Na(Ca) with amplitude (2.73+/-1.00)*10^-10 and (3.45+/-1.36)*10^-10 A, respectively.

The conclusion from these studies is that intracellular solution alkalization leads to significant decrease of salivary gland secretory cell membrane inward Na⁺-Ca²⁺ exchange current amplitude in Chironomus plumosus L. larva and in several cases to change of its direction. These changes could be connected with character of interactions between Na⁺ and Ca²⁺ ions and Na⁺-Ca²⁺ exchanger molecule. That’s why we examined how the influence of alkalization on Na⁺-Ca²⁺ exchanger functioning depends on changes in Na⁺ and Ca²⁺ gradients.

Fig.2 demonstrates how the influence of intracellular solution alkalization to pH 9.0 on Na⁺-Ca²⁺ exchange current is effected by Na⁺ gradient. According to results shown in Fig.2 the decrease of [Na⁺]_e leads to reduction of I_Na(Ca) amplitude at pH_i 9.0. intracellular solution alkalization to pH 9.0 at [Na⁺]_e 136.9, 68.4 and 16.0 mmol/l caused significant reduction of I_Na(Ca) amplitude by (50.05+/-6.60), (78.72+/-5.39) and (96.48+/-3.52)%, respectively. Moreover, alkalization to pH_i 9.0 at [Na⁺]_e 68.4 and 16 mmol/l evoked in three and five cases from six (respectively) biphasic current changes. In these cases amplitude of outward phase was (1.09+/-0.09)*10^-10 and (2.22+/-0.38)*10^-10 A, respectively.

In order to investigate how intracellular alkalization effects on Na⁺-Ca²⁺ exchange current depends on Ca²⁺ gradient we changed extracellular Ca²⁺ concentration. Preliminary studies of [Ca²⁺]_e influence on Na⁺-Ca²⁺ exchange current at physiological levels of pH showed that increase of [Ca²⁺]_e from 1 to 10 mmol/l evoked hyperbolic elevation of I_Na(Ca) amplitude (Fedirko, Klevets, Manko, 1997). As we discovered in this study (see Fig.3) intracellular solution alkalization to pH 9.0 in conditions of extracellular Ca²⁺ concentration change from 1.76 to 10 mmol/l led to significant decrease of Na⁺-Ca²⁺ exchange current amplitude by (55.57+/-5.39) and (72.38+/-10.22)%, respectively. Moreover, in two cases from seven at [Ca²⁺]_e 1.76 mmol/l, pH_i 9.0 and in three cases at [Ca²⁺]_e 10 mmol/l and pH_i 9.0 the biphasic changes of Na⁺-Ca²⁺ exchange current were observed. Amplitudes of outward phases were (2.27+/-0.61)*10^-10 and (3.38+/-0.27)*10^-10 A, respectively.

 

 

Discussion Board

Any Comment to this presentation?

[ABSTRACT] [INTRODUCTION] [METHODS] [RESULTS] [IMAGES] [DISCUSSION] [CONCLUSIONS] [REFERENCES] [Discussion Board]

---

	[Endocrinology]	[Physiology]

OLGA LARINA, Volodimir Manko
Copyright © 1999-2000. All rights reserved.

Last update: 13/01/00