Agonist-evoked alkaline shift in the cytosolic pH set point for activation of Na+/H+ antiport in human platelets. The role of cytosolic Ca2+ and protein kinase C.
This work examines the roles of elevated cytosolic Ca2+ and stimulation of protein kinase C in agonist and non-agonist-mediated alkaline shift of the cytosolic pH set point for activation of Na+/H+ antiport in human platelets. Ca2(+)-depleted and control platelets were subjected to phorbol 12-myristate 13-acetate, thrombin, vasopressin, and ionomycin in 1 mM or Ca2+ free, nominally bicarbonate free media. To measure the cytosolic pH set point for Na+/H+ antiport activation, cells were acidified to different levels using the sodium propionate method. In some experiments protein kinase C was inhibited by staurosporine. Both protein kinase C stimulation and elevation of cytosolic Ca2+ can produce an alkaline shift in the pH set point for activation of Na+/H+ antiport in human platelets. However, the effect of Ca2+i on the pH set point predominates that of protein kinase C stimulation. Cytosolic Ca2+ is a prerequisite for agonist-evoked alkaline shift in the cytosolic pH set point for activation of Na+/H+ antiport. The cytosolic Ca2+ level is also essential for maintaining the basal cytosolic pH. These findings underscore the central role of cytosolic Ca2+ under basal and stimulated states in regulating cytosolic pH of human platelets.
Kimura
M
M
Hypertension Research Center, University of Medicine and Dentistry of New Jersey, Newark 07103.
Gardner
J P
JP
Aviv
A
A
D000470:Alkaloids / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D002352:Carrier Proteins / Q000097:blood*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000097:blood; D017923:Sodium-Hydrogen Exchangers; D019311:Staurosporine; D013917:Thrombin / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D000470:Alkaloids; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D014667:Vasopressins; D015759:Ionomycin; D011493:Protein Kinase C; D013917:Thrombin; D019311:Staurosporine; D002118:Calcium