Biphasic response to human galanin of extracellular acidification in humanBowes melanoma cells

The metabolic response of galanin GAL1 receptor subtype, endogenously expre ssed in human Bowes melanoma (HBM) cells, was investigated. Cytosensor micr ophysiometry was used to determine the extracellular acidification rate. A biphasic response, consisting of a rapid increase in the extracellular acid ification rate followed by a decrease below the basal level, was observed a fter perfusion with human galanin. The magnitude and the rate of onset of b oth phases were dependent on the galanin concentration. The increase in the extracellular acidification rate (maximurn of 25% of basal level; -log(EC5 0)= 7.23 +/- 0.14) was transient, whereas the following decrease (maximum o f 40% of basal level; - log(EC50) = 7.77 +/- 0.23) was sustained. The EC50 values for the increase and decrease were in a similar range. After consecu tive galanin administration, the magnitude of the response was the same as for the unexposed cells, indicating the absence of galanin receptor desensi tization or internalization in HBM cells. Responses were blocked by pretrea tment with pertussis toxin and phorbol- 12-myristate- 13-acetate (PMA), ind icating a G-protein/protein kinase C signalling pathway. Our microphysiomet ry results show a biphasic response of the extracellular acidification rate mediated by the,galanin receptor expressed in HEM cells which has not been described previously for any other endogenously expressed neuropeptide rec eptor. (C) 2001 Elsevier Science B.V. All rights reserved.