IONIC CHANNELS IN DISSOCIATED SMOOTH MUSCLE CELLS

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The purpose of this proposal is to investigate in smooth muscle the membrane channels responsible for transmembrane ionic currents and the control of these channels by membrane potential, neurotransmitters, ions, metabolites and other agents. Since these ionic channels control the membrane potential, underly the action potential and are responsible for Ca++ entry into the cell, they play a central role in the control of smooth muscle contraction, a topic of considerable therapeutic importance (e.g., in hypertension, vasopasm, uterine and gastrointestinal contractility). Fundamental questions about the control of these ionic channels remain unanswered, however, because of experimental problems associated with the coupling of smooth muscle cells into a functional electrical syncytum with narrow, tortuous intercellular spaces and with the admixture of neural elements in the tissue. To circumvent these difficulties, we shall employ a preparation of freshly dissociated (as opposed to cultured) smooth muscle cells to which we shall apply the following techniques: 1.) recordings of membrane potential under "current clamp" conditions; 2.) voltage-clamp of the entire cell membrane; 3.) patch clamp recording of current flowing through single ionic channels; 4.) equilibrium and rapid kinetic binding of radiolabelled neurotransmitters and related agents. The selectivity, rectifying properties, kinetics of activation and inactivation and the control of these parameters by membrane potential and various agents will be studied for each of a variety of channels. From these studies there should emerge a more basic understanding of the electrical activity of smooth muscle and of those ionic channels common to smooth muscle and other cell types.