RIN14B: a pancreatic delta-cell line that maintains functional ATP-dependent K+ channels and capability to secrete insulin under conditions where it no longer secretes somatostatin

The delta-cell line RIN14B was characterized with regard to ATP-regulated K+ (K-ATP) channel activity and hormone release, By applying the patch-clamp technique, dose-response curves for ATP and the sulfonylurea tolbutamide were obtained in inside-out patches, The concentration causing half-maximal K-ATP channel inhibition was found to be 23.7 and 27.6 mu M for ATP and tolbutamide, respectively, ADP and diazoxide stimulated K-ATP channel activity, an effect dependent on the presence of intracellular Mg2+. The stimulatory effect of diazoxide also required the presence of ATP, The kinetic properties of the K-ATP channel were analysed in the presence of ATP, a combination of ADP and ATP and in nucleotide-free solutions, The distribution of K-ATP channel open time could be described by a single exponential function with a time constant of approximately 30 ms in nucleotide-free and in ATP-containing solutions, The presence of both GTP and ADP resulted in the appearance of an additional time constant of > 150 ms, Single-channel unitary current-voltage (i-V) relation was characterised for the K-ATP channel present in RIN14B cells, The slope conductance, measured at the reversal potential was found to be 19.1 +/- 2.4 pS. The permeability for K+ ions was calculated to be 0.31x10(-13) cm(3).s(-1). We have not been able to confirm the somatostatin releasing profile of the RIN14B cells using radioimmunoassays, nor could me find positive somatostatin stain with immunocytochemical techniques, We conclude that the RIN14B cell line, previously characterized as a somatostatin-secreting cell line, contains K-ATP channels with properties closely resembling the K-ATP channel described in the pancreatic beta-cell. However, the cell line appears to have dedifferentiated with regard to the ability to secrete somatostatin, maintaining the highly differentiated function of both insulin biosynthesis and exocytosis. (C) 1997 Federation of European Biochemical Societies.