Neurokinin A receptors are coupled to calcium mobilization in transfected fibroblasts

Desensitization of neurokinin A receptors expressed by B82 fibroblasts

After chronic exposure to neurokinin A, a time-dependent and recoverable desensitization of inositol monophosphate accumulation occurred in B82 fibroblasts transfected with cDNAs encoding for the bovine stomach NK2 receptor. Desensitized cells also showed decreased Ca2+ mobilization. While NK2 receptor antagonists had no effect on inositol monophosphate accumulation, substance P and senktide both produced a small degree of desensitization.

Effects of ethanol exposure on neuropeptide-stimulated calcium mobilization in N1E-115 neuroblastoma

The effects of acute and chronic (100 mM for 7 days) ethanol exposures on resting intracellular free calcium, [Ca2+]i as well as bradykinin and neurotensin mediated [Ca2+]i mobilization were determined in intact N1E-115 neuroblastoma. [Ca2+]i was monitored fluorometrically with the calcium indicator, fluo-3/AM. Acute exposure to ethanol resulted in an inhibition of bradykinin mediated [Ca2+]i mobilization with significant effects observed only at 400 mM ethanol. Neurotensin mediated [Ca2+]i mobilization was not significantly affected by any of the ethanol concentrations tested. Similarly, resting [Ca2+]i (64 +/- 2 nM) was unaffected by either chronic or acute ethanol as high as 400 mM. However, chronic exposure to ethanol significantly reduced the magnitude of bradykinin mediated [Ca2+]i mobilization both in the absence and presence of extracellular [Ca2+]. In contrast, [Ca2+]i mobilization in the presence of various concentrations of neurotensin was not significantly affected by chronic ethanol exposure. The results suggest that neuropeptide mediated [Ca2+]i mobilization is relatively insensitive to the acute presence of ethanol. In addition, chronic ethanol exposure appears to have selective effects on receptor mediated [Ca2+]i mobilization because this response to bradykinin, but not neurotensin, was significantly reduced in cells exposed to ethanol. The results also suggest that the reduction in bradykinin stimulated [Ca2+]i mobilization in chronically exposed cells is due in part to an inhibition of the release of intracellularly bound [Ca2+].

Demonstration of a neurokinin A receptor subtype in transfected fibroblasts

In competitive radioligand binding assays, the NK2 receptor antagonists [Tyr5,D-Trp6,8,9,Arg10]NKA(4-10) (MEN 10207) and [Tyr5,D-Trp6,8,9,Arg10]NKA(3-10) (MEN 10208) had high and low affinity, respectively, in bovine stomach membranes and SKLKB82#3 cells, a murine fibroblast cell line transfected with a cDNA encoding for the bovine NK2 receptor. These antagonists also had different affinities when inhibiting neurokinin A-induced polyphosphoinositide hydrolysis in SKLKB82#3 murine fibroblasts. Thus, the de novo protein expressed by the SKLKB82#3 murine fibroblasts may represent a distinct NK2 receptor subtype.