Regulation of M-Type Potassium Current by Intracellular Nucleotide Phosphates

Abstract

The effects of intracellular application of various concentrations of adenine nucleoside phosphates and nucleotide analogs on the M-type K current (IM) of single neurons isolated from sympathetic ganglia were studied. With 1 mM MgATP intracellularly IM decreased to 25% of its initial level 39 min after the start of whole-cell recording. In the absence of ATP the current decreased more rapidly. Addition of glucose and pyruvate extracellularly was equivalent to adding 1 mM MgATP intracellularly. AMP-PNP, a nonhydrolyzable ATP analog, at a concentration of 1 or 3 mM was unable to maintain IM in the absence of ATP. When ATP and AMP-PNP were combined in the pipette, however, the maintenance of IM was prolonged. A series of nucleotides and analogs have been combined with ATP to test for their ability to maintain IM and to alter calcineurin phosphatase activity. There was a positive correlation between the ability of a nucleotide to prevent the rundown of IM and its ability to inhibit calcineurin phosphatase activity. These findings show that the amplitude of IM is dually regulated by cellular levels of adenine nucleotide diphosphates and triphosphates. A hydrolyzable form of ATP is necessary to maintain the M current. The maintenance of IM is further enhanced by the simultaneous presence of ADP or other adenine nucleotides that alter calcineurin activity, but not by higher concentrations of ATP alone. These results are consistent with regulation of IM by phosphorylation events that maintain IM and dephosphorylation events that lead to current rundown.

Cholinergic Suppression of KCNQ Channel Currents Enhances Excitability of Striatal Medium Spiny Neurons

“…Electrophysiological studies of these neurons have not yielded evidence of their expression either. However, KCNQ channels are very sensitive to disruption of the intracellular milieu, as might occur with conventional electrophysiological approaches (Simmons and Schneider, 1998). In our hands, whole-cell dialysis of medium spiny neurons led to the loss of KCNQ-like currents in minutes.…”

Inhibitory modulation of distal C‐terminal on protein kinase C‐dependent phospho‐regulation of rat TRPV1 receptors

“…In a subset of experiments, the pipette solution was added with calcium buffers, including 5 m m EGTA, 10 m m 1,2‐bis(2‐aminophenoxy)ethane‐ N , N , N ′, N ‐tetra‐acetic acid (BAPTA) or 10 m m EGTA with 8 m m Ca 2+ (140 n m free Ca 2+ ; MaxChelator, Stanford University). Although the pipette solution contained no ATP, the relatively high concentration of extracellular glucose was used to maintain intracellular ATP (Simmons & Schneider, 1998). The bath and pipette solutions for single‐channel recordings in oocytes were symmetrical and contained 100 m m sodium gluconate and 10 m m NaCl instead of 140 m m NaCl, and other components were the same as the Ca 2+ ‐free bath solution for HEK 293 cells.…”

Histamine promotes excitability in bovine adrenal chromaffin cells by inhibiting an M-current

“…The observation that the sustained depolarization was either absent or smaller in amplitude in open-tip whole-cell configuration may reflect the presence of a soluble intracellular messenger in the pathway causing inhibition of the M-channels (see Marrion, 1997). However, other studies have shown that the M-current is sensitive to the availability of hydrolysable ATP (Simmons & Schneider, 1998), or that these currents are not observed with opentip whole-cell configuration (Xu & Adams, 1992), so it is also possible that the disturbance of the intracellular milieu inherent to the open-tip patch recording technique may prevent the observation of the effects of histamine on the M-current.…”