AJP - Cell Physiology, Vol 258, Issue 4 C739-C748, Copyright © 1990 by American Physiological Society
Combined force and voltage measurement in rapidly superfused guinea pig heart cells
N. Shepherd and V. J. Fisher
Research Service, Veterans Affairs Medical Center, New York, New York.
We describe the construction and use of a setup that allows the rapid
exchange of the solution surrounding an isolated guinea pig heart cell
while simultaneously measuring the isometric force and membrane potential
(Em). Cells were stably attached, by means of poly-L-lysine, to a force
transducer which was adapted from one previously used for a study of frog
atrial cells [N. Shepherd and F. Kavaler.Am. J. Physiol. 251 (Cell Physiol.
20): C653-C661, 1986]. The modified transducer is simple to construct and
use and can be readily added to existing patch-clamp setups. The strength
of attachment of a cell to the transducer exceeded the strength of the
gigaseal in all of the experiments. The membrane potential was measured by
means of patch electrodes and a high-impedance voltage follower. Rapidly
changing extracellular K concentration [( K]o) from 5.4 to 10.8 mM caused a
positive change of Em by 16.5 +/- 1.4 mV with a half-time (t1/2) of 27 +/-
4 ms. Replacing calcium in the perfusate by magnesium instantly abolished
the contraction and shortened the action potential. Twitch tension returned
stepwise to the control value on return of calcium to the perfusate. Our
initial observations show that the patch electrode can be used successfully
in conjunction with the isometric force transducer and rapid extracellular
solution changes for studies of excitation and contraction coupling in
isolated mammalian heart cells.
