The role of chlorine ion cotransport in the regulation of rest potential and osmotic homeostasis in eartearthworm somatic muscle cells

Ionic selectivity of chloride ion symport in mechanisms controlling resting potential and osmotic homeostasis in earthworm somatic muscle cells

“…Removal of Cl -ions from bathing solution or application of furosemide, a blocker of Cl -transfer, depolarized muscle cell membrane of earthworm similarly to inactivation of Na + /K + -pump with ouabain [3]. In our experiments, replacement of chlorides for bromides did not decrease RMP of somatic MC (Table 1).…”

“…Similarly, baclofen was inefficient after replacement of chloride with bromide ions in the bathing solution (Table 1). Thus, in this case the replacement of chlorides for bromides was equivalent to removal of Cl -ions from the solution [3,5] or exposure of the cells to furosemide, a blocker of Cl -transfer.…”

“…When chloride ions were replaced for bromides ones, HypoOS also depolarized the muscle membrane (Table 1). We previously showed that active Cl --symport is involved in the regulation of intracellular osmotic homeostasis, while changes in extracellular osmotic pressure modulate activity of Clsymport, thus affecting RMP of MC [3]. Under resting conditions, replacement of chlorides for bromides did not depolarize the muscle plasmalemma both in the absence of Cl -ions or in the presence of furosemide, but baclofen under the same conditions could not hyperpolarize the membrane, which indicates impossibility for Br -ions to compensate for the absence of Cl -ions.…”

“…The contribution of electrogenic ionic pumps into the integral value of resting membrane potential is high and reflects simultaneous work of two systems: Na + /K + -antiport and chloride symport [2,6]. We previously found that these systems possess two different membrane "transporters" and independent activation mechanisms [5], at the same time, these systems are closely related and inactivation of one system turns off its counterpart [3,5]. However, the selectivity of Cl -transfer in relation to the entire system of active transport of potential-generating ions remains unclear.…”