A comparison of non- XXXX receptor channels in type-2 astrocytes and granule cells from rat cerebellum.

@entity2227 @entity14425 @entity4176 @entity140 @entity143 @entity71377 @entity141
1. Patch-clamp recording methods have been used to compare the pharmacological properties and single-channel characteristics of non- @entity143 receptor channels in cerebellar type-2 astrocytes and granule cells. 2. In type-2 astrocytes whole-cell concentration-response curves for @entity2227 , @entity14425 , @entity140 and @entity4176 gave EC50 values of 5.8, 3.8, 7.6 and 160 microM and Hill slopes of 1.65, 1.18, 1.64 and 1.65, respectively, resembling estimates for granule cell receptors. 3. The non- @entity143 receptor antagonists CNQX and @entity71377 (see Methods) inhibited whole-cell @entity4176 currents in both cell types. The IC50 for CNQX antagonism of the @entity4176 response was 536 nM in type-2 astrocytes, and 500 nM in granule cells. The IC50 for @entity71377 was 3.5 microM in astrocytes and 3.7 microM in granule cells. 4. CNQX acted as a competitive antagonist of whole-cell @entity4176 responses in type-2 astrocytes and granule cells giving Schild plots with a slope near 1. The equilibrium constant, K, for CNQX binding was 524 nM in astrocytes and 489 nM in granule cells. 5. @entity14425 and @entity140 responses showed rapid desensitization in type-2 astrocytes with a ratio of steady-state to peak response of 0.09. Concanavalin A reduced this desensitization. 6. Non- @entity143 channels in type-2 astrocytes and granule cells showed a low permeability to @entity141 ions with a reversal potential, for @entity4176 -activated whole-cell currents in isotonic @entity141 , of approximately -25 mV for astrocytes and -45 mV for granule cells. 7. Outside-out patches from type-2 astrocytes exhibited a range of single-channel conductances that were superficially similar to the @entity2227 -activated conductances in granule cells. However, the type-2 astrocytes were devoid of @entity143 receptors, hence all of these conductances originated from non- @entity143 channels. Their slope conductances were approximately 11, 21, 32, 42 and 52 pS. Amplitudes were verified with mean low-variance plots and single-channel current-voltage curves, which were linear. 8. There was also evidence of lower conductance @entity4176 -activated channels in astrocyte patches. From noise analysis their estimated mean conductance was 1.9 pS, as described for the 'low-conductance' type @entity4176 responses in cerebellar neurones. 9. Apparent open times, shut times and burst lengths of @entity140 -activated (3-10 microM) channels were examined in patches from type-2 astrocytes, and kinetic properties of the 40 and 50 pS levels were compared with the lower levels. 10. Our results indicate some marked pharmacological similarities between non- @entity143 receptor channels in type-2 astrocytes and granule cells.(ABSTRACT TRUNCATED AT 400 WORDS)
