EGTA modulates equatorial currents in frog lenses.
A combination of a vibrating probe with microelectrodes was used to study the effects on the equatorial K+ current, J, of perturbing the frog lens by removing Ca2+ from the bathing medium. The results were different in the absence and presence of EGTA. In the absence of EGTA the reversal potential (PDJ = 0) remained near the Nernst potential; the input resistance, R, and the resistance of the segment of the K+ current loop being studied, RJ, decreased; the driving force (PD - PDJ = 0) increased; and J increased fourfold. In the presence of EGTA J did not increase more than twofold; the current-voltage relationship became linear; RJ did not decrease and both the PD and the reversal potential, PDJ = 0, became less negative with time. These findings, which are dependent on the use of the vibrating probe, were unexpected, and they were explored by studying the effects of removing Na+ from the medium. Substituting TMA for Na+ did not increase J. Removal of Ca2+ and the addition of EGTA to a Na+-free medium in which frog lenses were bathed resulted in a decrease in RJ, and an increase in J; J varied inversely with the concentration of Na+ in the medium. The changes were reversible. A mechanism to account for the changes is proposed.
Walsh
S
S
University of Connecticut Health Center, Farmington 06032.
Patterson
J W
JW
D000818:Animals; D002118:Calcium / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology*; D004594:Electrophysiology; D007908:Lens, Crystalline / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects; D011894:Rana pipiens / Q000502:physiology*; D012964:Sodium / Q000502:physiology
D015221:Potassium Channels; D004533:Egtazic Acid; D012964:Sodium; D002118:Calcium