The effect of potassium (K)-free medium on the stimulation of cyclic AMP (cAMP) production by arginine vasopressin (AVP) and forskolin was examined in rat renal papillary collecting tubule cells in culture. All experiments were performed in the presence of 3-isobutyl-l-methylxanthine (0·5 mmol/l). Cellular cAMP levels in response to 1 nmol and 0·1 μmol AVP/1 were 430·9 ± 42·1 (s.e.m.) and 501·8± 43·6 fmol/μg protein per 10 min respectively; these levels were significantly (P <0·01) higher than those in the vehicle-treated group (126·6 ± 23·3 fmol/μg protein per 10 min). The cellular cAMP response to 1 nmol AVP/1 was significantly attenuated after 24 and 72 h of exposure of cells to K-free medium, cellular concentrations of cAMP being 280·2 ± 37·1 and 233·0 ± 9·6 fmol/μg protein per 10 min respectively. The response of cAMP to AVP remained unchanged when the cells were preincubated with K-free medium for 1 h. Similarly, forskolin (20 nmol/l)-stimulated cellular cAMP production was also significantly impaired after 24 or 72 h of exposure of cells to K-free medium. When the cells preincubated in K-free medium were again exposed for 1 h to K-replete medium containing 5 mmol KC1/1, cellular cAMP production in response to AVP or forskolin recovered totally. Cellular protein and ATP content and cellular viability were not altered by exposure of cells to K-free medium for 24 h, and thus the impaired cAMP response to AVP or forskolin in the K-depleted cells was independent of altered cellular viability and source of ATP. The present results indicate that the K ion is an important factor for AVP– and forskolin-activated adenylate cyclase at the catalytic unit in the renal papillary collecting tubule cells.
J. Endocr. (1987) 113, 199–204
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