title: Kinetics of Ca2(+)-ATPase activation in platelet membranes of essential hypertensives and normotensives.
abstract: To explore the etiology of altered Ca metabolism in essential hypertension, we studied parameters, i.e., maximal initial reaction velocity (Vmax) and Michaelis constant (Km), of Ca activation kinetics of Ca2(+)-ATPase in membrane fractions (isolated by a sucrose gradient) from platelets of blacks and whites, 27 of whom were essential hypertensives, 17 of whom were normotensives with a family history of essential hypertension, and 10 of whom were normotensives without a family history of the disease. The Vmax of hypertensives was significantly lower than in normotensives without a family history of essential hypertension (hypertensives, 14.99 +/- 1.71 nmol Pi.mg protein-1.min-1; normotensives, positive family history, 22.67 +/- 3.17 nmol Pi.mg protein-1.min-1; normotensives, negative family history, 27.54 +/- 4.37 nmol Pi.mg protein-1.min-1; overall, P = 0.0078). The Km was lower in both hypertensives and normotensives with a positive family history of essential hypertension as compared with normotensives with a negative family history of the disease (hypertensives, 1.70 +/- 0.23 microM; normotensives, positive family history, 1.38 +/- 0.2 microM; normotensives, negative family history, 2.79 +/- 0.58 microM; overall, P = 0.0251). Furthermore, the Km in whites was inversely related to plasma renin activity (r = 0.50; P less than 0.005). We propose that a lower Vmax for Ca2(+)-ATPase may play a role in the higher level of free Ca in platelets of essential hypertensives and that a higher affinity of the enzyme to Ca may reflect a process compensating for the lower Vmax. We also suggest that a higher Km for Ca2(+)-ATPase in juxtaglomerular cells of whites would result in blunting the release of renin.
authors: Hypertension Research Center, University of Medicine and Dentistry of New Jersey, Newark 07103.
authors: J
authors: J
authors: Takaya
authors: N
authors: N
authors: Lasker
authors: R
authors: R
authors: Bamforth
authors: M
authors: M
authors: Gutkin
authors: L H
authors: LH
authors: Byrd
authors: A
authors: A
authors: Aviv
mesh_terms: D000328:Adult; D044383:Black People; D001792:Blood Platelets / Q000201:enzymology*; D001794:Blood Pressure; D015992:Body Mass Index; D000252:Calcium-Transporting ATPases / Q000097:blood*; D002462:Cell Membrane / Q000201:enzymology; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D014481:United States; D044465:White People; D001741:Black or African American
chemical_list: D000252:Calcium-Transporting ATPases