Aromatic aldehydes and aromatic ketones open ATP-sensitive K+ channels in guinea-pig ventricular myocytes

How wasting is saving: weight loss at altitude might result from an evolutionary adaptation

At extreme altitude (>5,000 – 5,500 m), sustained hypoxia threatens human function and survival, and is associated with marked involuntary weight loss (cachexia). This seems to be a coordinated response: appetite and protein synthesis are suppressed, and muscle catabolism promoted. We hypothesise that, rather than simply being pathophysiological dysregulation, this cachexia is protective. Ketone bodies, synthesised during relative starvation, protect tissues such as the brain from reduced oxygen availability by mechanisms including the reduced generation of reactive oxygen species, improved mitochondrial efficiency and activation of the ATP-sensitive potassium (K_ATP) channel. Amino acids released from skeletal muscle also protect cells from hypoxia, and may interact synergistically with ketones to offer added protection. We thus propose that weight loss in hypoxia is an adaptive response: the amino acids and ketone bodies made available act not only as metabolic substrates, but as metabolic modulators, protecting cells from the hypoxic challenge.

Alchemy in the soup: transforming metabolic signals to excitability

The intersection of cell metabolism with electrical signaling links the environment and cell function over time scales ranging from milliseconds to lifetimes. In responding to cellular metabolites, adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels are an important component of this intersection. Recent studies have begun to delineate the roles of K(ATP) channels in multiple tissues and the far-reaching consequences of aberrant K(ATP) channel activity and disturbed sensing of cell metabolism.

Quantitative Analysis of the Marker Compounds in Salvia miltiorrihiza Root and Its Phytomedicinal Preparations

A HPLC method is described in order to separate and identify 4 phenolic compounds including lithospermic acid B, 3,4-dihydroxyphenyllactic acid (danshensu), rosmarinic acid, and protocatechuic aldehyde as well as 3 lipophilic ones (tanshinone I, tanshinone II(A) and cryptotanshinone) from the roots of Salvia miltiorrihiza or the herbal product containing S. miltiorrihiza available in Chinese or Japanese market. The influence of extractive conditions, such as method, solvents and time, on the 4 phenolic marker components in S. miltiorrihiza is well discussed. In order to investigate the stability of lithospermic acid B, the preparation samples of an injection and a granule were analyzed after being stored at 4 degrees C, 20 degrees C and 40 degrees C for up to six months.

Functional evidence for a glibenclamide-sensitive K+ channel in rat ileal smooth muscle

The motor activity of gastrointestinal smooth muscle is closely related to the membrane potential. Controlling the membrane potential via modulation of K+ channels is essential for the action of neurotransmitters on smooth muscle. In the present study the effect of the K+ channel activator, lemakalim, on longitudinal smooth muscle of the rat ileum was investigated. Segments of rat ileum were stimulated by the muscarinic receptor agonist, carbachol (10(-6) M). Lemakalim (10(-10) to 3 x 10(-5) M) induced a dose-dependent inhibition of the carbachol-induced contraction. This inhibitory effect of lemakalim was not modified by neural blockade with tetrodotoxin (10(-6) M, n = 9). Glibenclamide (10(-7) to 10(-5) M), a specific blocker of ATP-dependent K+ channels antagonized dose dependently the relaxant effect of lemakalim (IC50: 3.4 x 10(-6) M, n = 11, P < 0.001). In contrast, apamin (10(-7) M, n = 9, n.s.) and charybdotoxin (10(-7) M, n = 9, n.s.), specific blockers of Ca2+-dependent K+ channels and the non-specific K+ channel blocker, tetraethylammonium (10(-4) to 10(-1) M), had no influence on the inhibitory effect of lemakalim. Contractions induced by the Ca2+ channel activator, Bay-K-8644, were completely inhibited by lemakalim (10(-5) M, n = 12). This inhibitory effect was also selectively antagonized by glibenclamide (10(-5) M). Potential non-adrenergic non-cholinergic (NANC) inhibitory mediators like ATP, nitric oxide (NO) or neurotensin showed no sensitivity to glibenclamide. These functional data indicate that the relaxant effect of lemakalim is due to a specific activation of glibenclamide-sensitive K+ channels, which in turn can modulate the activity of dihydropyridine-sensitive (voltage-dependent) Ca2+ channels. A physiological or pathophysiological role of the glibenclamide-sensitive K+ channels in intestinal smooth muscle is discussed; however, they seem not to be involved in the effect of the NANC inhibitory mediators tested.

Stilbene disulfonates block ATP-sensitive K+ channels in guinea pig ventricular myocytes

Effects of stilbene disulfonates on single KATP channel currents were investigated in inside-out and outside-out membrane patches from guinea pig ventricular myocytes. All drugs tested, 4,4'-diisothiocyanatostilbene,2,2'-disulfonic acid (DIDS), 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS), and 4,4'-diaminostilbene-2,2'-disulfonic acid (DADS), inhibited the KATP channel when they were applied to the intracellular, but not extracellular side of the membrane patch. Inhibitory actions of DIDS and SITS were irreversible, whereas those induced by DNDS and DADS were reversible. KATP channel inhibition was concentration dependent with an order of potency of DIDS > SITS approximately DNDS > DADS; the Hill coefficient was close to unity for each drug. No change in channel conductance was observed during exposure to DIDS or DNDS; however, channel kinetics was altered. Distribution of the open time within bursts and that between bursts could be described by a single exponential relation in the absence and presence of DIDS or DNDS. The time constant of the open time within bursts was not altered, but that between bursts was decreased by DIDS (from 40.0 +/- 8.1 to 29.8 +/- 6.7 msec, P < 0.05) and by DNDS (from 43.1 +/- 9.3 to 31.9 +/- 7.1 msec, P < 0.05). Distributions of closed time within bursts were also fitted to a single exponential function both in the absence and presence of drugs, while those of the closed time between bursts were fitted to a single exponential function in the absence of drugs, but a double exponential function was required in the presence of drugs. The rates of onset and development of channel inhibition by DIDS and DNDS appeared to be concentration dependent; a longer time was required to reach a new steady-state of channel activity as drug concentration was decreased. Inhibition by DIDS or DNDS was regulated by intracellular pH; inhibition was greater during acidic conditions. For DIDS (0.1 mM), the open probability (Po) expressed as a fraction of the value before drug application was 42.9 +/- 8.3% at pH 7.4 and 8.2 +/- 6.6% at pH 6.5 (P < 0.01); corresponding values for DNDS (1 mM) were 39.6 +/- 17.6 and 8.9 +/- 5.8%, respectively (P < 0.01). From these data, we conclude that stilbene disulfonates block the KATP channel by binding to their target site with one-to-one stoichiometry. Similar to glibenclamide, the binding of stilbene disulfonates may reflect interpolation in an "intermediate lipid compartment" between the cytosolic drug and the site of drug action.

Activation and reactivation of the ATP-sensitive K+ channel of the heart can be modified by drugs

Activation and reactivation of the ATP-sensitive K+ channel (IK.ATP) were studied with the patch-clamp technique in guinea-pig ventricular myocytes. The K+ channel openers, nicorandil and pinacidil, activated IK.ATP in an internal ATP-dependent manner. Both drugs increased the open probability of IK.ATP without changing the channel conductance. They prolonged lifetimes of bursts and shortened interburst intervals without influencing the fast gating within bursts. These effects were the opposite of those of internal ATP. However, the interaction between ATP and either nicorandil or pinacidil appeared not to be simple competition. We found that three carbonyl compounds--3,4-dihydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde, and 2,4-dihydroxyacetophenone--could activate IK.ATP through an intracellular mechanism that was dependent upon the presence of ADP and Mg2+. It has been suggested that these three carbonyl compounds bind covalently to proteins to form a Schiff base, which may be responsible for their effects upon IK.ATP. Internal application of the proteolytic enzyme trypsin prevented both the spontaneous and Ca(2+)-induced rundown of the KK.ATP channel. Tryptic digestion did not change either the channel's sensitivity to inhibition by ATP nor the fast gating kinetics of IK.ATP. Internal application of an exopeptidase, carboxypeptidase A, but not leu-aminopeptidase, prevented the spontaneous and Ca(2+)-induced rundown of the IK/ATP channel, effects similar to those of trypsin treatment. These results suggest that the target site of trypsin digestion may be located on the carboxy (C)-terminal of the channel proteins or associated regulatory units.