ENHANCEMENT OF QUANTAL TRANSMITTER RELEASE AND MEDIATOPHORE EXPRESSION BY CYCLIC-AMP IN FIBROBLASTS LOADED WITH ACETYLCHOLINE

Neuronal properties such as neurotransmitter uptake and release can be expressed in non-neuronal cells. We show here that fibroblasts-mouse cell line L-M(TK-)-are able to take up acetylcholine from the external medium and to release it in response to a calcium influx. Release was assessed biochemically by a luminescence method, but it was also elic ited from individual fibroblasts and recorded in real-time using a Xen opus myocyte as an acetylcholine detector. After treatment for three t o six days with dibutyryl-cyclic AMP, the cells changed their shape an d acetylcholine release was greatly enhanced. Surprisingly, in differe ntiated fibroblasts the time-course transmitter release exhibited a hi gh degree of variability even for the successive responses evoked from the same cell; many currents recorded in myocytes on electrical stimu lation of fibroblasts had an extremely long duration (up to 1 s or mor e). This suggested that the release sites were kept open for a very lo ng time. Cyclic AMP treatment also caused a marked increase in the exp ression of mediatophore 16,000 mel. wt proteolipid in fibroblast membr anes. Mediatophore is an acetylcholine-translocating protein which is abundant in cholinergic presynaptic plasma membranes. It is concluded that cyclic AMP differentiation of fibroblasts prolongs the duration o f acetylcholine release at individual sites and enhances the expressio n of the 16,000 mel. wt proteolipid-forming mediatophore. Copyright (C ) 1996 IBRO.