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Bulletin of Experimental Biology and Medicine, Vol. 145, No. 5, May, 2008
549
PHYSIOLOGY
Ionic Selectivity of Chloride Ion Symport in Mechanisms Controlling Resting Potential and Osmotic Homeostasis in Earthworm Somatic Muscle Cells
E. M. Volkov, M. E. Volkov, and A. L. Zefirov
Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 145, No. 5, pp. 484-486, May, 2008 Original article submitted January 31, 2008
Replacement of Cl for Br in bathing solution did not reduce resting potential and had no effect on modulation of transmembrane potential in hyper- and hypoosmotic solutions. Under these conditions, baclofen, an agonist of GABAergic B-type receptors, failed to activate Na+/K+-pump in earthworm somatic muscle cells. It was hypothesized that the contribution of Cl symport to osmotic homeostasis is not highly selective in respect to replacement of Cl to Br ions, whereas in case of activation of electrogenic ion pumps, this replacement is equivalent to removal of Cl ions from the bathing solution.
Key Words: muscle cells; ionic pump; chloride symport; earthworm
In addition to Na+/K+-pump, active symport of chlo-ride ions exists in muscle cells (MC) of earthworm musculocutaneous sac and is involved in the regulation and maintenance of resting membrane potential (RMP) [1,6]. 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.
Our aim was to study the contribution of active anion symport into RMP and osmotic regulation of
somatic MC under conditions of replacement of chlorides for bromides.
MATERIALS AND METHODS
Experiments were carried out during autumn-winter period on MC of longitudinal fascicles from the inner side of musculocutaneous sac of Lumbricus terrestris earthworm. Freshly isolated fragments of musculocutaneous sack...