Some hormonal effects on myocardial phosphate efflux

Area of Science:

• Cardiovascular Physiology
• Cellular Signaling
• Biochemistry

Background:

• Cellular phosphate (Pi) transport is crucial for cardiac function.
• Hormonal regulation of ion flux in the heart is not fully understood.
• Lactate dehydrogenase (LDH) release indicates cell membrane integrity.

Purpose of the Study:

• To investigate the effects of 23 agonists on cellular 32P efflux and LDH release in a perfused rat heart model.
• To characterize the dose-dependent and time-dependent responses of various compounds on Pi transport and cell damage.
• To explore potential mechanisms underlying hormonal modulation of cardiac Pi efflux.

Main Methods:

• Perfused rat heart preparation pre-labeled with 32P.
• Measurement of 32P efflux and LDH release following administration of 23 different agonists.
• Dose-response and time-course analysis of agonist effects.

Main Results:

• Thirteen compounds induced detectable changes in Pi efflux or LDH release at high doses within 10 minutes.
• Catecholamines and glucagon initially stimulated Pi efflux, then inhibited it, and increased LDH release.
• Insulin and corticosteroids altered Pi efflux with varying recovery rates; some increased LDH release.
• Carbachol transiently stimulated Pi efflux without significant LDH release.
• Dibutyryl cyclic GMP had no effect, while ouabain stimulated Pi efflux without inotropic effects.

Conclusions:

• Hormonal effects on Pi efflux are diverse and often polyphasic.
• Pi efflux likely involves electroneutral NaH2PO4 transport across the cardiac plasmalemma.
• Intracellular Na+, pH, and Pi concentrations may mediate many observed hormonal effects on cardiac Pi transport and cell integrity.