Biophysical Journal 72: 691-697 (1997)
© 1997 the Biophysical Society

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Adaptation of Single Cardiac Ryanodine Receptor Channels

Patricio Vélez ^*, Sandor Györke ^#, Ariel L. Escobar , Julio Vergara ^¶ and Michael Fill ^*

Loyola University Chicago, Maywood, Illinois 60153 USA
Texas Tech University, Lubbock, Texas 79430 USA
Centro de Biofísicas y Bioquímica, Instituto Venezolano de Investigación Científica, Caracas, Venezuela
University of California, Los Angeles, CA 90024 USA

ABSTRACT

Single cardiac ryanodine receptor (RyR) channel adaptation was previously defined with Ca²⁺ stimuli produced by flash photolysis of DM-nitrophen (caged-Ca⁺²). Photolysis of DM-nitrophen induced a very fast Ca⁺² overshoot (Ca⁺² spike) at the leading edge of the Ca⁺² stimuli. It has been suggested that adaptation ( 1.3 s) may reflect Ca⁺² slowly coming off the RyR Ca⁺² activation sites following the faster Ca⁺² spike ( 1 ms). This concern was addressed by defining the Ca²⁺ deactivation kinetics of single RyR channels in response to a rapid reduction in free Ca²⁺ concentration ([Ca²⁺]_FREE). The [Ca²⁺]_FREE was lowered by photolysis of Diazo-2. Single RyR channels deactivated ( 5.3 ms) quickly in response to the photolytically induced [Ca²⁺]_FREE reduction. Improved estimates of the Ca²⁺ spike time course indicate that the Ca²⁺ spike is considerably faster (10-100-fold) than previously thought. Our data suggest that single RyRs are not significantly activated by fast Ca²⁺ spikes and that RyR adaptation is not due to deactivation following the fast Ca²⁺ spike. Thus, RyR adaptation may have an important impact on Ca²⁺ signaling in heart.

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