SUMMARY1. Using whole-cell and single channel recordings, we have examined the properties of acetylcholine (ACh)-activated currents in neurones from larval and pupal Drosophila melanogaster (fruit fly), larval and embryonic Musca domestica (house fly), and nymphal Schistocerca gregaria (locust).2. In all preparations, single channel recordings revealed two major classes of ACh-activated channels, with average conductances of approximately 32 and 59 pS. 5. The whole-cell dose-response curve suggests that activation of current by ACh increases up to at least 100 ftM and that multiple ligand binding steps are involved.6. Drosophila and Musca larval neuronal ACh-activated channels show some unique features in their cholinergic pharmacological properties: (a) they are only weakly activated by the potent neuromuscular nicotinic agonist suberyldicholine, (b) hexamethonium and decamethonium are weak, but approximately equi-effective blockers, and (c) a-and K-bungarotoxin (BTX) both blocked reversibly, though o-BTX appears to be the more potent inhibitor.

1. K+ conductances were characterized in isolated, identified superior colliculus-projecting (SCP) rat visual cortical neurons. SCP neurons were identified in vitro under epifluorescence illumination after in vivo retrograde labeling with rhodamine-labeled microspheres or "beads." For experiments, SCP neurons were isolated from the primary visual cortex of postnatal day 7 to 16 (P7-P16) Long Evans rat pups after bead injections into the ipsilateral superior colliculus at p5. 2. Recording conditions were optimized to allow the characterization of Ca2+ -independent K+ conductances. SCP cells that were largely devoid of processes were selected for recording, and experiments were completed 2-30 h after cell isolation. Ca2+ -independent, depolarization-activated K+ currents were routinely recorded during 200-ms voltage steps to potentials positive to -50 mV from a holding potential of -70 mV. 3. Peak outward current densities and the relative amplitudes of the peak and plateau outward currents evoked during 200-ms voltage steps varied among SCP cells. Although cells were isolated from animals at different ages (P7-P16) and maintained for varying times in vitro (2-30 h), no correlations were found between the variations in peak current densities or peak to plateau current ratios and the age of the animal from which the cell was isolated or the length of time the cell was maintained in vitro before recording. 4. Pharmacological experiments revealed the coexpression of three K+ current components in SCP cells that could be separated on the basis of differing sensitivities to the K+ channel blockers, 4-aminopyridine (4-AP) and tetraethylammonium (TEA). Varying the concentration of 4-AP, for example, facilitated the separation of two rapidly activating K+ currents similar to A (IA) and D(ID) type currents in other cells. ID in SCP neurons is blocked by micromolar concentrations of 4-AP, whereas micromolar concentrations of 4-AP are required to effect complete block of IA in these cells. The current component remaining in the presence of high concentrations (5-10 mM) of 4-AP is slowly activating outward K+ current, similar to delayed rectifier (IK) currents in other cells. IK in SCP neurons is blocked by micromolar concentrations of TEA. 5. Activation of IA, ID, and IK in SCP neurons is voltage dependent, although the three current components display distinct time- and voltage-dependent properties. For example, although both IA and ID begin to activate at approximately -50 mV, IA activates two to three times faster than ID. In addition, the threshold for activation of IK (-30 mV) is approximately 20 mV depolarized from that of IA (or ID), and the voltage dependence of IK activation is steeper than that of IA and ID.(ABSTRACT TRUNCATED AT 400 WORDS)

1 Conductance increases to -y-aminobutyric acid (GABA) were recorded in the gm6b and opener muscle of the spiny lobsters, Panulirus interruptus and P. argus. 2 GABA-evoked responses were insensitive to picrotoxin at concentrations as high as 5 x 10-5 M. Some blockade by picrotoxin was observed at higher concentrations. 3 In normal physiological saline, the reversal potential of the Panulirus GABA-induced response was near the resting potential. The reversal potential was unaffected by reductions in sodium and calcium. Reduction of chloride by 50% resulted in a greater than 10 mV shift in the reversal potential of the GABA-induced response. 4 Muscimol was able to mimic the action of GABA while baclofen was without effect. Bicuculline was a weak blocker.5 Avermectin Bla irreversibly increased the chloride permeability of the gm6b membrane. This conductance increase was blocked by picrotoxin over a range of concentrations similar to those required for blockade of the GABA-induced response. 6 GABA-induced responses of the gm6b muscle of Homarus americanus were blocked almost completely by picrotoxin 10-6 M.7 Sensitivity to picrotoxin is not invariably associated with GABA-activated chloride-mediated conductance increases. It is suggested that alteration in the binding-site for picrotoxin on the GABAactivated chloride-ion channel does not change other functional characteristics of the GABA-induced response.

Specimens of the stone crab, Menippe mercenaria, survived severe hypoxia (PO2 less than 8mm Hg) for at least 12 hr at 28-30 degrees C. During the time course of 12 hr of hypoxia, hemolymph L-lactate levels rose to 30-50 mumoles/g wet wt. There was a slight elevation of L-alanine levels, whereas succinate was found in only trace quantities in the hemolymph. Pronounced metabolic changes took place in the heart, cheliped closer, and leg socket muscles during severe hypoxia. L-lactate accumulated to levels ranging from 16-20 mumoles/g wet wt. There were pronounced changes in high-energy phosphate levels in the cheliped closer and leg socket muscles. Taking into account expected intra- and extracellular water content, the calculated intracellular lactate content in the three muscles investigated is substantially less than the hemolymph lactate concentrations. Part of this reverse concentration gradient may be accounted for by the reduction in lactate activity due to cation-lactate complex formation. Hemolymph calcium and magnesium concentrations rose considerably during severe hypoxia. During recovery from severe hypoxia, approximately 50% of the accumulated lactate in the hemolymph was cleared in 6 hr. Hemolymph lactate and alanine levels returned to near control levels after 24 hr of recovery. This study shows that the stone crab, M. mercenaria, survives severe hypoxia by a reliance on glycogen fermentation to lactate. This species is capable of tolerating high levels of accumulated lactate.

SUMMARY Jejunal absorption of sodium and water has been investigated in 10 normal Indians and 11 patients with chronic tropical sprue. Normal saline and solutions containing amino acids and dipeptides were studied. In both groups little absoprtion of sodium and water from normal saline was seen. Mean water and sodium absorption from the free amino acid or dipeptide solutions showed no significant difference between the groups and was similar to absorption from normal saline. These results differ from data obtained in normal English subjects where at these concentrations significant stimulation of sodium and water absorption was seen. In a proportion of subjects in both groups net secretion was observed. However, no 30 November 1976 Methods Studies were performed in 10 normal Indians and 11 patients with tropical sprue, described in a previous report (Hellier et al., 1976b). Both groups of subjects were chosen from the same village area. The diets in the two groups were comparable, seven of the 10 normal subjects and eight of the 11 sprue patients being vegetarians. In the sprue patients the diets were considered to be poor or very poor in four, good in two, and fair in the remainder. In the normal subjects diets were poor in two, good in three, and fair in the remainder. The mean weights in the normal and sprue group were 43-6 kg (range 35-60 2 kg) and 38-4 kg (range 33 3-50 4 kg) respectively. Serum albumin levels were low in three of the sprue patients but in none of the normal subjects. The mean stool volume in the sprue patients was 764 ± 262 ml and in the normal subjects 580 ± 175 ml. The difference in mean stool volume was significant (p < 0-025). None of the subjects studied had intestinal parasites or evidence of other infections. The normal Indians all had normal vitamin B12 absorption and faecal fat excretion and all but three had normal xylose absorption. All patients with tropical sprue had chronic disease (of more than six months' duration), and were not suffering from high volume watery diarrhoea at the time of the study. All had abnormal results for xylose and 480 on 11 May 2018 by guest. Protected by copyright.