Activation of a non-specific cation conductance by intracellular injection of inositol 1,3,4,5-tetrakisphosphate into identified neurons of Aplysia.
The ionic mechanism of the effect of intracellularly injected inositol 1,3,4,5-tetrakisphosphate (IP4) on the membrane of identified neurons (R9-R12) of Aplysia kurodai was investigated with conventional voltage-clamp, pressure injection, and ion-substitution techniques. Intracellular injection of IP4 into a neuron voltage-clamped at -45 mV reproducibly induced a slow inward current (20-60 s in duration, 3-5 nA in amplitude) associated with a conductance increase. The current was decreased by depolarization and increased by hyperpolarization. The extrapolated reversal potential was -21 mV. The IP4-induced inward current was sensitive to changes in the external Na+, Ca2+ and K+ concentration but not to changes in Cl- concentration, and was resistant to tetrodotoxin (50 microM). When the cell was perfused with tetraethylammonium (5 mM) but not with 4-aminopyridine (5 mM), the IP4-induced inward current recorded at -45 mV slightly increased. The IP4-induced inward current was partially reduced by calcium channel blockers (Co2+ and Mn2+). These results suggest that intracellularly injected IP4 can activate a non-specific cation conductance.
Sawada
M
M
Department of Physiology, Shimane Medical University, Izumo, Japan.
Ichinose
M
M
Maeno
T
T
D000818:Animals; D001048:Aplysia / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*
D007295:Inositol Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate