Phosphoinositides in giant barnacle muscle fibers: A quantitative analysis at rest and following electrical stimulation

Abstract

Quantitative data are presented on the composition of the major phospholipids in isolated giant barnacle muscle fibers. It is shown, using internal perfusion techniques, that the high specific activity of labeling of polyphosphoinositides in vivo is attained by the activities of specific kinases. Electrical stimulation causes a reduction in the specific activity of labeling of PtdInsP 2. This phospholipid, which is the immediate precursor for the release of InsP 3, is found at a significant concentration (40 nmol/g wet weight) in single barnacle muscle fibers, sufficient to support a role as precursor of second messengers. The rapid catabolization of PtdInsP 2 in the absence of external Ca 2+ suggests that E-C coupling in barnacle muscle may be associated with a voltage-dependent, Ca 2+-independent, activation of the breakdown of polyphosphoinositides.