Influences of pressure-injected cyclic AMP on the membrane current and characteristics of an identified neuron of Aplysia kurodai.
The ionic mechanism of the effect of intracellularly injected adenosine 3',5'-cyclic monophosphate (cAMP) on the membrane of identified neuron L5 of Aplysia kurodai was investigated with conventional voltage-clamp and ion-substitution techniques. The intracellular elevation of cAMP caused an inward current (IcAMP), which was not accompanied by a significant change in membrane conductance at potentials more hyperpolarized than -60 mV. The current increased over the voltage range (-50 to -30 mV) associated with a conductance decrease and decreased at potentials more hyperpolarized than -60 mV. Elevated intracellular cAMP was found to enhance a region of negative slope resistance in steady-state I-V relations. Duration of the IcAMP was greatly prolonged by bath-applied isobutylmethylxanthine (50 microM), but imidazole (10 mM) had an opposite effect on the IcAMP. Tolbutamide (5 mM), a protein kinase inhibitor, reduced the IcAMP. The current was not affected by the presence of bath-applied TTX (50 microM), ouabain (50 microM), or triaminopyrimidine (5 mM). Reduction of [Na+]0 reversibly decreased the IcAMP. Li+ could largely substitute for Na+. Alterations of [K+]0, and bath application of 4-AP (5 mM) and TEA (30 mM) did not affect the IcAMP. In the presence of Na+, Cl-, and divalent cations such as Ca2+ and Ba2+ inhibited the IcAMP. These results suggest that fast elevation of intracellular cAMP induces a TTX-resistant slow Na+ inward current, and the current might be due to activation of cAMP-dependent protein kinase.
Hara
N
N
Sawada
M
M
Maeno
T
T
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001048:Aplysia; D003080:Cold Temperature; D000242:Cyclic AMP / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005944:Glucosamine / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011073:Polyamines; D011312:Pressure; D011743:Pyrimidines; D013779:Tetrodotoxin / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology
D007093:Imidazoles; D011073:Polyamines; D011743:Pyrimidines; D013779:Tetrodotoxin; D004533:Egtazic Acid; D010042:Ouabain; C029899:imidazole; D014044:Tolbutamide; D000242:Cyclic AMP; D005944:Glucosamine; D015056:1-Methyl-3-isobutylxanthine