A mechanogated nonselective cation channel in proximal tubule that is ATP sensitive

Abstract

Ion channels that are gated in response to membrane deformation or “stretch” are empirically designated stretch-activated channels. Here we describe a stretch-activated nonselective cation channel in the basolateral membrane (BLM) of the proximal tubule (PT) that is nucleotide sensitive. Single channels were studied in cell-intact and cell-free patches from the BLM of PT cells that maintain their epithelial polarity. The limiting inward Cs+ conductance is ∼28 pS, and channel activity persists after excision into a Ca2+- and ATP-free bath. The stretch-dose response is sigmoidal, with half-maximal activation of about −19 mmHg at −40 mV, and the channel is activated by depolarization. The inward conductance sequence is: NH[Formula: see text] ∼ Cs+ ∼ Rb+> K+ ∼ Na+ ∼ Li+ > Ca2+ ∼ Ba2+> N-methyl-d-glucamine ∼ tetraethylammonium. The venom of the common Chilean tarantula, Grammostola spatulata, completely blocks channel activity in cell-attached patches. Hypotonic swelling reversibly activates the channel. Intracellular ATP concentration ([ATP]i) reversibly blocks the channel (inhibitory constant ∼0.48 mM), suggesting that channel function is coupled to the metabolic state of the cell. We conclude that this channel may function as a Ca2+ entry pathway and/or be involved in regulation of cell volume. We speculate this channel may be important when [ATP]i is depleted, as occurs during periods of increased transepithelial transport or with ischemic injury.