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]

DISCUSSION

 

We found that salivary gland secretory cell Na⁺-Ca²⁺ exchange in Chironomus plumosus L. larva is sensitive not only to changes of extracellular pH level but also to changes of intracellular pH level.

In particular reduction of extracellular pH level evoked decrease of I_Na(Ca) amplitude that conforms to preliminary studies (Klevets et al., 1996). This effect perhaps could be explained by the protonation of acid groups (COO^- ) of aminoacid residues, which participate in binding Na⁺ by exchanger molecule.

Acidification of intracellular solution caused insignificant decrease of Na⁺-Ca²⁺ exchange current. On our opinion, it is possible in conditions of absence of competition between Ca²⁺ and H⁺ for intracellular cation binding transport site of exchanger.

The fact that reduction of I_Na(Ca) amplitude at simultaneous intra- and extracellular acidification was statistically unauthentic, testify that functioning of Na⁺-Ca²⁺ exchanger in direct mode is more dependent on level of intracellular pH.

Obtained results show that intracellular solution alkalization leads to decrease of inward Na⁺-Ca²⁺ exchange current amplitude. Moreover, in several cases direction of I_Na(Ca) changes from inward to outward. These changes of I_Na(Ca) could be explained by change in dissociation-association processes of Na⁺ and Ca²⁺ with exchanger molecule. We suppose that intracellular solution alkalization leads to decrease of competition between H⁺ and Na⁺ for interior cation binding transport site. It aggravates sodium dissociation from and possibly simultaneously aggravates calcium association with this site. As result Na⁺-Ca²⁺ exchange begin to go along Ca²⁺ gradient but no along Na⁺ gradient. That is reason of decrease of I_Na(Ca) and change of its direction.

It is necessary to point out that changes of Na⁺-Ca²⁺ exchanger functioning in conditions of intracellular solution alkalization at decrease and liquidation of sodium gradient are more significant.

More significant changes of salivary gland secretory cell plasma membrane Na⁺-Ca²⁺ exchanger functioning were also evoked by intracellular solution alkalization at increase of Ca²⁺ gradient.

Discussion Board

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

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	[Endocrinology]	[Physiology]

OLGA LARINA, Volodimir Manko
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Last update: 13/01/00