A mechanosensitive K+ channel in heart cells. Activation by arachidonic acid.

Abstract

Mechanosensitive ion channels have been described in many types of cells. These channels are believed to transduce pressure signals into intracellular biochemical and physiological events. In this study, the patch-clamp technique was used to idendfy and characterize a mechanosensitive ion channel in rat atrial cells. In cell-attached patches, negative pressure in the pipette activated an ion channel in a pressure-dependent manner. The pressure to induce half-maximal activation was 12 -3 mmHg at +40 mV, and nearly full activation was observed at ~20 mmHg. The probability of opening was voltage dependent, with greater channel activity at depolarized potentials. The mechanosensitive channel was identical to the K + channel previously shown to be activated by arachidonic acid and other lipophilic compounds, as judged by the outwardly rectifying current-voltage relation, single channel amplitude, mean open time (1.4 +-. 0.3 ms), bursty openings, K + selectivity, insensitivity to any known organic inhibitors of ion channels, and pH sensitivity. In symmetrical 140 mM KC1, the slope conductance was 94 -+ 11 pS at +60 mV and 64 -8 pS at -60 mV. Anions and cations such as CI-, glutamate, Na +, Cs +, Li +, Ca 2+, and Ba 2+ were not permeant. Extracellular Ba ~+ (1 raM) blocked the inward K + current completely. GdCI3 (100 tiM) or CaCI2 (100 wM) did not alter the K + channel activity or amplitude. Lowering of intracellular pH increased the pressure sensitivity of the channel. The K + channel could be activated in the presence of 5 mM intracellular [ATP] or 10 IzM glybenclamide in inside-out patches. In the absence of ATP, when the ATP-sensitive K + channel was active, the mechanosensitire channel could further be activated by pressure, suggesting that they were two separate channels. The ATP-sensitive K + channel was not mechanosensitive. Pressure activated the K + channel in the presence of albumin, a fatty acid binding protein, suggesting that pressure and arachidonic acid activate the K + channel via separate pathways.

Desensitization of mechano-gated K 2P channels

“…Stretch-activated K ϩ channels are present in neurons of both the central and the peripheral nervous systems (7)(8)(9), and they also have been described in nonnervous tissue including the heart and gastrointestinal tract (4,(10)(11)(12). In rat atria, the mechanosenstive K ϩ currents decline to a plateau of 20-30% of peak within Ϸ1 s (4).…”

The Mechanosensitive Ca2+ Channel as a Central Regular of Prostate Tumor Cell Migration and Invasiveness

“…In particular, both display the same cation selectivity, both are blocked by amiloride and Gd 3+ , both are insensitive to flufenamic and niflumic acid, and both have a single channel conductance of ∼25 pS (i.e., when measured in symmetrical 140 mM K + and 2 mM external Ca 2+ ). Because MTX is a highly amphipathic molecule (Escobar et al 1998), it may activate MscCa by changing bilayer mechanics, as has been proposed for other amphipathic agents that activate or modulate MS channel activity (Martinac et al 1990;Kim 1992;Casado andAscher 1998, Perozo et al 2002). …”

“…In particular, using siRNA and antisense strategies to reduce endogenous TRPC4 expression, TRPC4 was shown to be required for AA-induced Ca 2+ oscillations but not for SOC function. This AA activation may have implications for the mechanosensitivity of TRPC4 since AA has been show to activate/modulate a variety of MS channels by directly altering the mechanical properties of the bilayer surrounding the channel (Kim 1992;Casado and Ascher 1998;Patel and Honoré 2001). Since AA is produced by PLA 2 , which is itself MS (Lehtonen and Kinnunen 1995), TRPC4 may derive its mechanosensitivity from this enzyme in addition to possibly being directly sensitive to bilayer stretch.…”

Biophysical and Structural Studies of Escherichia coli Mechanosensitive Channel of Large Conductance in Lipid Bilayers

“…This is speculated to be due to a suggested relatively small conformational change required for channel activation, and probably has a physiological role of allowing quantitative response to the stimulus. Interestingly, the TRAAK channel also activates in the presence of polyunsaturated fatty acids and arachidonic acid (Fink et al, 1998;Kim, 1992), suggesting a close relationship between channel activity and phospholipids.…”

“…Starting with the identification of TRAAK in rat atrial cells in 1992 (Kim, 1992(Kim, , 1993, new eukaryotic mechanosensitive channels have steadily been identified, a trend which continues. Apart from MscL and MscS, which had already been discussed, three families have been identified as having eukaryotic mechanosensitive channels as members: K2P, Trp, and Piezo channels.…”