[Effect of microinjection of GABA into the caudate nucleus on electrical discharges of nociceptive neurons in caudate nucleus of rat].

The characteristics of glass microelectrode recorded electrical activity of nociceptive neurons in the caudate nucleus elicited by microinjection of GABA and blockage by picrotoxin (PIC) were studied in 53 Wistar rats. The results showed that GABA (25, 50, 100 micrograms/2 microliters every 2 min) inhibited the activity of pain excitation neurons (PEN), as shown by decreased frequency and increased latency, but enhanced the activity of pian, inhibition neurons (PIN), as shown by shortened duration and increased discharge frequency. Both activities are highly dose-dependent and could be blocked by PIC (i.p. 250 micrograms, 1 ml/1 min).

Effects of protein tyrosine kinase and protein tyrosine phosphatase on apical K(+) channels in the TAL.

We have previously demonstrated that the protein level of c-Src, a nonreceptor type of protein tyrosine kinase (PTK), was higher in the renal medulla from rats on a K-deficient (KD) diet than that in rats on a high-K (HK) diet (Wang WH, Lerea KM, Chan M, and Giebisch G. Am J Physiol Renal Physiol 278: F165-F171, 2000). We have now used the patch-clamp technique to investigate the role of PTK in regulating the apical K channels in the medullary thick ascending limb (mTAL) of the rat kidney. Inhibition of PTK with herbimycin A increased NP(o), a product of channel number (N) and open probability (P(o)), of the 70-pS K channel from 0.12 to 0.42 in the mTAL only from rats on a KD diet but had no significant effect in tubules from animals on a HK diet. In contrast, herbimycin A did not affect the activity of the 30-pS K channel in the mTAL from rats on a KD diet. Moreover, addition of N-methylsulfonyl-12,12-dibromododec-11-enamide, an agent that inhibits the cytochrome P-450-dependent production of 20-hydroxyeicosatetraenoic acid, further increased NP(o) of the 70-pS K channel in the presence of herbimycin A. Furthermore, Western blot detected the presence of PTP-1D, a membrane-associated protein tyrosine phosphatase (PTP), in the renal outer medulla. Inhibition of PTP with phenylarsine oxide (PAO) decreased NP(o) of the 70-pS K channel in the mTAL from rats on a HK diet. However, PAO did not inhibit the activity of the 30-pS K channel in the mTAL. The effect of PAO on the 70-pS K channel was due to indirectly stimulating PTK because pretreatment of the mTAL with herbimycin A abolished the inhibitory effect of PAO. Finally, addition of exogenous c-Src reversibly blocked the activity of the 70-pS K channel in inside-out patches. We conclude that PTK and PTP have no effect on the low-conductance K channels in the mTAL and that PTK-induced tyrosine phosphorylation inhibits, whereas PTP-induced tyrosine dephosphorylation stimulates, the apical 70-pS K channel in the mTAL.

Effects of erysimin G on renal tubular function and 70-pS K+ channel activity of thick ascending limb.

AIM: To study the effect of erysimin G (CH35H52O13) on the thick ascending limb (TAL) 70-pS K+ channel of rat kidney and its effect on diuresis. METHODS: The patch-clamp cell-attached recording technique was used to record the single potassium channel current, and the urine volume (UV) was measured by urethral intubation to determine the diuretic effect. RESULTS: Erysimin G can increase the urine volume and decrease the 70-pS potassium channel activity of TAL. CONCLUSION: Erysimin G has a diuretic effect and its inhibition on the activity of apical 70-pS potassium channel may be the mechanism of its diuretic effect.