[Properties of KATP channels in hippocampal CA1 pyramidal neurons from adult rats].

Properties of KATP channels in acutely dissociated hippocampal CA1 pyramidal neurons of adult rats were studied with inside-out patch-clamp technique. With symmetrical 140 mmol/L K+ on both sides of the excised membrane, the single-channel conductance was approximately 63 pS and the reversal potential was 1.71 mV. These channels had a weak inward rectifying property. Channels' openings interrupted by shorter closed intervals were more frequently observed at negative holding potential than at positive holding potential. However, noticeable voltage dependence was not found in channel open probability. ATP applied at the cytosolic side inhibited channel activity in a concentration-dependent manner with an IC50 of 0.1 mmol/L. Sulphonyluren tolbutamide (1 mmol/L), a specific KATP channel blocker, added to the bath completely suppressed the channel activity, while diazoxide (1 mmol/L), a KATP channel opener, had no apparent effect.

An adenosine triphosphate (ATP)-sensitive K+ channel of rat neocortical neurons is bi-gated by intracellular ATP and voltage: a novel channel gating mechanism?

To determine whether the adenosine triphosphate (ATP)-sensitive K+ (K-ATP) channels, which are suggested to be mainly regulated by intracellular ATP or other kinds of triphosphate nucleotides, are gated by membrane potentials (Vm), single K-ATP channel currents were studied on inside-out membrane patches of neurons acutely dissociated from Sprague-Dawley rat neocortex. The K-ATP channels recorded have a unitary conductance from 96.97 +/- 5.32 pS (n = 11) at potentials of approximately 10-60 mV to 98.31 +/- 3.26 pS (n = 11) at approximately -10 to -60 mV. Besides being inhibited by cytoplasmic ATP, channel kinetics was also affected by Vm. Open- and closed-time histograms were well fitted by 2 exponentials, suggesting that the channels have 2 open and closed states. Mean open time (tau om), open probability increased while mean closed time (tau cm) decreased with depolarization. The fitted equations of the relationships between Vm and those kinetic parameters may be described as: tau om = -159.26lnV + 403.64, Po = -0.01Vm2 + 0.08Vm + 0.87 and tau cm = 0.17Vm3-2.5Vm2 + 10.35Vm - 7.68, respectively. We suggest that the K-ATP channels be bi-gated by both intracellular ATP and membrane potentials. This property of the neuronal K-ATP channels may be related to their pathophysiological functions.

Rodent insulin receptors are immunologically different from other mammalian insulin receptors.

Four monoclonal antibodies (MA-5, MA-10, MA-20, and MA-51) and one polyclonal antibody (ARS-2) against human insulin receptor were used to immunoprecipitate the insulin receptor from several species which had been photolabeled with N epsilon B29-monoazido-benzoyl-[125I]iodoinsulin. All four monoclonal antibodies immunoprecipitated human insulin receptor from human placental membranes. MA-10 and MA-51, but not MA-5 or MA-20, immunoprecipitated insulin receptors from liver plasma membranes of rabbit, guinea pig, dog, cattle, pig, and chicken. None of the monoclonal antibodies immunoprecipitated insulin receptors of rat, mouse, hamster, or chinchilla. In contrast, all of the insulin receptors were immunoprecipitated by the polyclonal anti-insulin receptor antibody, ARS-2. MA-10 and MA-51 compared with [125I]iodoinsulin for binding to guinea pig and rabbit liver plasma membranes in a fashion similar to insulin, although less effectively. MA-51 also mimicked the action of insulin by stimulating lipogenesis and autophosphorylation of the insulin receptor beta subunit in isolated rabbit adipocytes. The results suggest that insulin receptors of mammals, other than rodent, share with human insulin receptor the same epitope(s) recognized by MA-10 and MA-51. Rodent insulin receptors, with the exception of guinea pig, are different. We speculate that the difference lies in the amino acid sequence 485-599 of the alpha subunit of the insulin receptor.