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]

INTRODUCTION

The Na⁺-Ca²⁺ exchanger is a countertransport mechanism located in the cell membrane. It was previously identified in heart muscle and in the squid giant axons more than thirty years ago (Reuter, Seitz, 1968; Baker et al., 1968). The Na⁺-Ca²⁺ exchanger was also found in cardiac muscle (Glitch et al., 1970), epithelia (Baker, 1972; Blaustein, 1974; Blaustein, Nelson, 1982), acinar cell plasma membrane (Bayerdoffer, Haase, Schultz, 1985; Grinkiv, Klevets, Shostakovskaya, 1988), salivary gland secretory cell membrane in Chironomus plumosus L. larva (Manko, Klevets, Fedirko, 1995; Klevets, Manko, Fedirko, 1995).

salivary gland secretory cell membrane Na⁺-Ca²⁺ exchange current in Chironomus plumosus L. larva was registered in response to the membrane hyperpolarization (Manko et al., 1995; Klevets et al., 1995). Slow inward current is evoked at E_Na=+54.6 mV and hyperpolarisating shifts (with duration 3-3.5 sec) of membrane potential from clamped level (-20 mV). It decreases at E_Na=0 mV and becomes outward at E_Na=-45 mV. Direction of current is determed by sign of Na⁺ transport motive force at clamped potential. This current depends on repolarising pulses value, [Ca²⁺]_e (Fedirko et al., 1995) and [Ca²⁺]_i that is why it was identified as current of Na⁺-Ca²⁺ exchange.

In spite of significant progress in the investigation of secretory cell membrane Na⁺-Ca²⁺ exchanger its structure and functional peculiarities is not thoroughly identified. So he investigation of these topics still remains actual. Full answer on questions about functional role of Na⁺-Ca²⁺ exchanger and its structure in certain tissue could be done only after discovery really specific blockators and modulators of Na⁺-Ca²⁺ exchange (Baker, 1986). That’s why investigations of blocators and mechanism of their effect on Na⁺-Ca²⁺ antiport system is inevitable step on the way to better understanding of exchanger’s structure and its functional role in secretory processes.

One of the well known modulators of Na⁺-Ca²⁺ exchange in different types of cells is level of pH. Cytoplasmic protons as previously reported is a potent inhibitor of Na⁺-Ca²⁺ exchange current in guinea-pig giant patch (Doering, Lederer, 1991 a,b). Moreover, Ca²⁺ transport mediated by Na⁺-Ca²⁺ exchange is very sensitive to change of pH (Doering, Lederer, 1993) and is modulated by it (Philipson et al., 1982). Alkalization of cytoplasmic solution from pH 7.2 to pH 8.0 evokes a large, biphasic increase in Na⁺-Ca²⁺ exchange current. A stepwise acidifying of intracellular pH (7.2 – 6.4) causes a biphasic, but monotonic decrease in Na⁺-Ca²⁺ exchange current in guinea-pig heart cells. In addition, the slowly developing block is dependent on the presence of Na⁺ on the intracellular side (Doering, Lederer, 1994).

Modulative effect of pH on Na⁺-Ca²⁺ exchange current was also discovered in secretory cells.

Preliminary studies of extracellular H⁺ effect on salivary gland secretory cell membrane Na⁺-Ca²⁺ exchanger in Chironomus plumosus L. larva showed, that acidifying of extracellular solution led to reduction of Na⁺-Ca²⁺ exchange current. Extracellular solution alkalization caused contrary effect (Klevets, Manko, Fedirko, 1996). In present report we examined the effect of intra- and extracellular H⁺ on salivary gland secretory cell membrane Na⁺-Ca²⁺ exchange and its dependence on Na⁺ and Ca²⁺ gradients.

 

 

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