The effects of pentylenetetrazol on molluscan neurons. II. Voltage clamp studies

The effects of pentylenetetrazol (PTZ) upon the steady and transient outward ionic currents during PTZ-induced prolonged depolarizations were investigated using voltage clamp techniques. PTZ causes a 5-35% reduction in gL and a 40-60% reduction in steady-state gK. There is also a marked reduction in the activation of gA of Connor and Stevens6 at all clamp potentials; a shortening of the time constant for the inactivation of gA; and a 10-15 mV shift in the depolarizing direction of the curve relating the steady-state inactivation of gA to membrane potential. The equilibrium potentials for both gA and gK are depolarized by 20 mV in PTZ solution. Equation and voltage clamp data for normal repetitive firing were integrated with the normal and PTZ-alered data. Solution to these equations demonstrated: (1) normal repetitive firing in response to a constant current stimulus; and (2) PTZ-altered repetitive firing that was in the direction of, and for the most part, similar to the observed behavior.     

Renal toxicity. Tobramycin and gentamicin

To see if urinary 2-methyl-4-chlorophenoxyacetic acid (MCPA) excretion could be used to estimate MCPA exposure, four healthy males ingested 5 mg MCPA. The MCPA in the urine was extracted and anlyzed by high pressure liquid chromatography. About 50% of the ingested dose was detected in the urine within 48 h. On the fifth day after intake the MCPA concentration in the urine was below the level of detection, 0.2 microgram/ml. The MCPA did not increase those serum enzymes indicating liver cell damage (S-alanine-aminotransferase, S-alkaline-phosphate). Some creatine kinase (CK) and S-aspartate-aminotransferase (ASAT) values were pathological, but, as all CK values were normal in two persons and all ASAT values were normal in three persons, it not likely that MCPA had a toxic effect on muscle cells. MCPA in urine seems to be a useful indicator of MCPA intake in humans. All the urine passed within 48 h of MCPA exposure must be collected.