Catecholamine sensitive adenylate cyclase activity in different segments of the rabbit nephron

Abstract

The sensitivity to catecholamines of the adenylate cyclase (AC) activity contained in single tubule samples was investigated on 10 different well defined segments, isolated by microdissection from collagenase treated rabbit kidneys. No responsiveness to isoproterenol (10(-6) M) was observed in the proximal tubule (convoluted and straight portions), the thin descending and thick ascending limbs of the loop of Henle, and the first ("bright") portion of the distal convoluted tubule (DCTb); in contrast high responses (stimulation factors: 4 to 6 fold) were obtained in the second ("granular") portion of the distal convoluted tubule (DCTg), as well as in both the "granular" (CCTg) and the "light" (CCTl) portions of the cortical collecting tubule. In absolute value, however, the CCTl response was definitely lower than those measured in DCTg and CCTg, as is its control activity. In the medullary portion of the collecting tubule, the AC response to isoproterenol was rather poor both in absolute and relative terms. Dose-response curves measured on DCTg samples indicated a threshold response with an isoproterenol concentration below 10(-8) M; half maximal effect corresponded to about 3 x 10(-8) M. CCTl sensitivity to isoproterenol was of the same order of magnitude. Isoproterenol as well as norepinephrine effects in DCTg and CCTl were completely suppressed by 10(-4) M propranolol, indicating that the observed AC stimulation was mediated via receptors of the beta type. In beta blocked CCTl, 10(-6) M norepinephrine did not inhibit vasopressin-induced AC stimulation; in the presence of 10(-6) M norepinephrine, 10(-4) M phentolamine resulted in no additional AC stimulation in DCTg and CCTl; these data suggest the absence of alpha receptors inhibiting AC activity in these structures. In DCTg, AC stimulation induced either by 10(-6) M isoproterenol or by 1 U/ml PTH were observed to be additive when the two hormones were given together. The presence of catecholamine-dependent AC activity in three distal portions of the rabbit nephron is discussed in relation to its possible physiological implications.