An active electrical response, the hyperpolarizing activation or H.A. response, is characteristic of L cells (a continuous line of fibroblasts) and is transmitted in a decremental manner between contiguous cells. Direct electrical coupling between pairs of L cells occurs occasionally, but transmission of the active electrical response is not dependent on such electrical connections. Some L cells are sensitive to acetylcholine but the transmitted response is not dependent on a cholinergic mechanism. 5-Iodosalicylate blocks the active electrical response. The response can be elicited readily by mechanical stimuli, and thus can serve both as a mechanical and chemical receptor mechanism and as a means of communication between cells.

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