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Beta-adrenergic induced potassium current in Xenopus oocyte: involvement of cyclic AMP
Abstract:
The effect of a beta-adrenergic agonist, on full-grown Xenopus oocytes, still surrounded by their ovarian envelopes, has been studied by electrophysiological methods. The oocytes were hyperpolarized by isoproterenol. Under voltage clamp, the elicited outward current reversed at a membrane potential of - 95 mV, a value close to the K+ equilibrium potential. The isoproterenol induced current varied linearly with the membrane potential in the range studied (- 120 mV, - 30 mV). Half-maximum current was obtained at 3.10(-8) M isoproterenol. Propranolol (10(-7) M) completely suppressed the response to isoproterenol (10(-9) to 10(-5) M). 8-Br-cAMP induced a current which also reversed at - 95 mV. Methyl-isobutyl-xanthine (MIX), a potent inhibitor of phosphodiesterases, potentiated the current induced by isoproterenol. These experiments strongly suggest that the increase in K+ permeability due to catecholamines is mediated by cAMP.
Insights
Beta-adrenergic agonists like isoproterenol increase potassium permeability in Xenopus oocytes. This effect is mediated by cyclic AMP (cAMP) and blocked by propranolol.
Area of Science:
- Cellular electrophysiology
- Molecular signaling in Xenopus oocytes
Background:
- Xenopus oocytes are a model system for studying ion channel regulation.
- Beta-adrenergic agonists are known to affect cellular processes through various signaling pathways.
Purpose of the Study:
- To investigate the electrophysiological effects of beta-adrenergic agonists on Xenopus oocytes.
- To elucidate the signaling mechanism underlying catecholamine-induced changes in ion permeability.
Main Methods:
- Electrophysiological recordings (voltage clamp) on full-grown Xenopus oocytes.
- Application of isoproterenol, propranolol, 8-Br-cAMP, and methyl-isobutyl-xanthine (MIX).
Main Results:
- Isoproterenol induced hyperpolarization and an outward current reversible at -95 mV (close to K+ equilibrium potential).
- The isoproterenol-induced current was dose-dependent and blocked by propranolol.
- 8-Br-cAMP mimicked the effect of isoproterenol, and MIX potentiated the response, suggesting cAMP mediation.
Conclusions:
- Catecholamine-induced increase in K+ permeability in Xenopus oocytes is mediated by cyclic AMP (cAMP).
- This study provides evidence for a cAMP-dependent signaling pathway regulating ion channels in amphibian oocytes.