Voltage-gated potassium (KV) channels represent an important dilator influence in the cerebral circulation, but the composition of these tetrameric ion channels remains unclear. The goals of the present study were to evaluate the contribution of KV1 family channels to the resting membrane potential and diameter of small rat cerebral arteries, and to identify the alpha-subunit composition of these channels using patch-clamp, molecular and immunological techniques. Initial studies indicated that 1 micromol l(-1) correolide (COR), a specific antagonist of KV1 channels, depolarized vascular smooth muscle cells (VSMCs) in pressurized (60 mmHg) cerebral arteries from -55 +/- 1 mV to -34 +/- 1 mV, and reduced the resting diameter from 152 +/- 15 microm to 103 +/- 20 microm. In patch clamped VSMCs from these arteries, COR-sensitive KV1 current accounted for 65 % of total outward KV current and was observed at physiological membrane potentials. RT-PCR identified mRNA encoding each of the six classical KV1 alpha-subunits, KV1.1-1.6, in rat cerebral arteries. However, only the KV1.2 and 1.5 proteins were detected by Western blot. The expression of these proteins in VSMCs was confirmed by immunocytochemistry and co-immunoprecipitation of KV1.2 and 1.5 from VSMC membranes suggested KV1.2/1.5 channel assembly. Subsequently, the pharmacological and voltage-sensitive properties of KV1 current in VSMCs were found to be consistent with a predominant expression of KV1.2/1.5 heterotetrameric channels. The findings of this study suggest that KV1.2/1.5 heterotetramers are preferentially expressed in rat cerebral VSMCs, and that these channels contribute to the resting membrane potential and diameter of rat small cerebral arteries.

Voltage-gated potassium (K V ) channels represent an important dilator influence in the cerebral circulation, but the composition of these tetrameric ion channels remains unclear. The goals of the present study were to evaluate the contribution of K V 1 family channels to the resting membrane potential and diameter of small rat cerebral arteries, and to identify the a-subunit composition of these channels using patch-clamp, molecular and immunological techniques. Initial studies indicated that 1 mmol l _1 correolide (COR), a specific antagonist of K V 1 channels, depolarized vascular smooth muscle cells (VSMCs) in pressurized (60 mmHg) cerebral arteries from _55 ± 1 mV to _34 ± 1 mV, and reduced the resting diameter from 152 ± 15 mm to 103 ± 20 mm. In patch clamped VSMCs from these arteries, COR-sensitive K V 1 current accounted for 65 % of total outward K V current and was observed at physiological membrane potentials. RT-PCR identified mRNA encoding each of the six classical K V 1 a-subunits, K V 1.1-1.6, in rat cerebral arteries. However, only the K V 1.2 and 1.5 proteins were detected by Western blot. The expression of these proteins in VSMCs was confirmed by immunocytochemistry and co-immunoprecipitation of K V 1.2 and 1.5 from VSMC membranes suggested K V 1.2/1.5 channel assembly. Subsequently, the pharmacological and voltage-sensitive properties of K V 1 current in VSMCs were found to be consistent with a predominant expression of K V 1.2/1.5 heterotetrameric channels. The findings of this study suggest that K V 1.2/1.5 heterotetramers are preferentially expressed in rat cerebral VSMCs, and that these channels contribute to the resting membrane potential and diameter of rat small cerebral arteries.

The essential oil of catnip, Nepeta cataria L., contains two isomers of nepetalactone, E,Z-and Z,Enepetalactone, and was tested for repellent activity to adult male German cockroaches, Blattella germanica (L.), in a choice-test arena. The two isomers of nepetalactone were purified by using preparative thin-layer chromatography and tested for behavioral activity in the choice-test arena. Significant differences due to concentration were detected by analysis of variance, and the responses were compared by least-squared means analysis. The activities of the essential oil and purified isomers were compared with N,Ndiethyl-3-methylbenzamide (DEET) by a paired t-test. E,Z-Nepetalactone was the most active of the compounds tested, being significantly more active to this species than equivalent doses of DEET, the essential oil, or Z,E-nepetalactone. Antennectomized insects showed no response to concentrations that were active against intact insects. ABSTRACT The essential oil of catnip, Nepeta cataria L., contains two isomers of nepetalactone, E,Zand Z,E-nepetalactone, and was tested for repellent activity to adult male German cockroaches, Blattella germanica (L.), in a choice-test arena. The two isomers of nepetalactone were puriÞed by using preparative thin-layer chromatography and tested for behavioral activity in the choice-test arena. SigniÞcant differences due to concentration were detected by analysis of variance, and the responses were compared by least-squared means analysis. The activities of the essential oil and puriÞed isomers were compared with N,N-diethyl-3-methylbenzamide (DEET) by a paired t-test. E,Z-Nepetalactone was the most active of the compounds tested, being signiÞcantly more active to this species than equivalent doses of DEET, the essential oil, or Z,E-nepetalactone. Antennectomized insects showed no response to concentrations that were active against intact insects.

The cerebral arteries of hypertensive rats are depolarized and highly myogenic, suggesting a loss of K(+) channels in the vascular smooth muscle cells (VSMCs). The present study evaluated whether the dilator function of the prominent Shaker-type voltage-gated K(+) (K(V)1) channels is attenuated in middle cerebral arteries from two rat models of hypertension. Block of K(V)1 channels by correolide (1 micromol/l) or psora-4 (100 nmol/l) reduced the resting diameter of pressurized (80 mmHg) cerebral arteries from normotensive rats by an average of 28 +/- 3% or 26 +/- 3%, respectively. In contrast, arteries from spontaneously hypertensive rats (SHR) and aortic-banded (Ao-B) rats with chronic hypertension showed enhanced Ca(2+)-dependent tone and failed to significantly constrict to correolide or psora-4, implying a loss of K(V)1 channel-mediated vasodilation. Patch-clamp studies in the VSMCs of SHR confirmed that the peak K(+) current density attributed to K(V)1 channels averaged only 5.47 +/- 1.03 pA/pF, compared with 9.58 +/- 0.82 pA/pF in VSMCs of control Wistar-Kyoto rats. Subsequently, Western blots revealed a 49 +/- 7% to 66 +/- 7% loss of the pore-forming alpha(1.2)- and alpha(1.5)-subunits that compose K(V)1 channels in cerebral arteries of SHR and Ao-B rats compared with control animals. In each case, the deficiency of K(V)1 channels was associated with reduced mRNA levels encoding either or both alpha-subunits. Collectively, these findings demonstrate that a deficit of alpha(1.2)- and alpha(1.5)-subunits results in a reduced contribution of K(V)1 channels to the resting diameters of cerebral arteries from two rat models of hypertension that originate from different etiologies.