Effects of veratrine and tetrodotoxin on the frog lens potential in normal and calcium-free media.
The membrane potentials of posterior fibers of the isolated American bullfrog lens were measured in Ringer solution containing various external Ca2+ concentrations ([Ca]0) by using a conventional glass microelectrode technique. The reduction or removal of [Ca]0 evoked a rapid depolarization of the lens potential whereas the increase of [Ca]0 had almost no effects on the membrane potential. The magnitude of depolarization in Ca2+ -free medium was augmented by adding veratrine but reduced by either the addition of tetrodotoxin (TTX) or the reduction of external Na+ concentration. A slight depolarization still remained after the blockade of Na-channels by adding TTX and developed progressively during a successive exposure of lens to Ca2+-free media. It was concluded that veratrine-sensitive rapid and large depolarization in the frog lens fibers bathed in Ca2+-free medium results from a marked elevation of Na+ permeability but that the TTX-insensitive time-dependent depolarization may depend on the loss of K+ content in lens fibers.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D007552:Isotonic Solutions / Q000494:pharmacology; D007908:Lens, Crystalline / Q000187:drug effects*; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D011892:Rana catesbeiana; D000077331:Ringer's Solution; D013779:Tetrodotoxin / Q000494:pharmacology*; D014702:Veratrine / Q000494:pharmacology*
D007552:Isotonic Solutions; D013779:Tetrodotoxin; D000077331:Ringer's Solution; D014702:Veratrine; D008274:Magnesium; D002118:Calcium