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Journal of Experimental Biology 155,305-321 (1991)
Published by Company of Biologists 1991

Potassium and Calcium Currents in Dissociated Muscle Fibres of the Mollusc Philine Aperta

D. A. DORSETT ¹ and C. G. EVANS ¹

¹ Animal Physiology Group, School of Biological Sciences, University College North Wales Bangor, Gwynedd LL57 2UW, UK

Dissociated unstriated muscle fibres from the buccal mass retractor muscles of the mollusc Philine aperta were studied using a two-electrode voltage-clamp. The mean resting potential of the fibres was -76.3±0.44mV (N=30), and the membrane resistance was 42.2±3M. The space constant of the fibres was 2.03+0.33mm (N=5).

Three outward potassium currents were resolved in response to a depolarising step to zero from resting potential. (1) An early transient current, voltageactivated and blocked by 2 mmoll^-1 4-aminopyridine (4-AP). This resembled the A-current described in molluscan neurones and some arthropod muscle fibres. (2) A calcium-dependent late transient current, with slower kinetics, which was suppressed by 50 mmoll^-1 tetraethylammonium chloride (TEA-Cl), zero-calcium saline, 1 mmol^-1 Cd²⁺ and 1 µmoll^-1 verapamil. (3) A delayed voltage-activated current, blocked by 50 mmoll^-1 TEA-Cl and with kinetics associated with the delayed rectifier current I_K.

An inwardly directed current, blocked by zero-calcium salines, Cd²⁺ and verapamil, was considered to be a calcium current whose activation closely matched that of the Ca²⁺-dependent potassium current.

A blockade of either the A-current, or exposure to low-calcium artificial sea water, or a combination of both, promoted the development of oscillations and regenerative spikes in the muscle fibre following depolarization

Key words: mollusc, muscle, potassium currents, calcium current, spiking, Philine aperta

Accepted on August 1, 1990

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