Small arteries exhibit tone, a partially contracted state that is an important determinant of blood pressure. In arterial smooth muscle cells, intracellular calcium paradoxically controls both contraction and relaxation. The mechanisms by which calcium can differentially regulate diverse physiological responses within a single cell remain unresolved. Calcium-dependent relaxation is mediated by local calcium release from the sarcoplasmic reticulum. These 'calcium sparks' activate calcium-dependent potassium (BK) channels comprised of alpha and beta1 subunits. Here we show that targeted deletion of the gene for the beta1 subunit leads to a decrease in the calcium sensitivity of BK channels, a reduction in functional coupling of calcium sparks to BK channel activation, and increases in arterial tone and blood pressure. The beta1 subunit of the BK channel, by tuning the channel's calcium sensitivity, is a key molecular component in translating calcium signals to the central physiological function of vasoregulation.

We present the cloning and characterization of two novel calcium-activated potassium channel ␤ subunits, hKCNMB3 and hKCNMB4, that are enriched in the testis and brain, respectively. We compare and contrast the steady state and kinetic properties of these ␤ subunits with the previously cloned mouse ␤1 (mKCNMB1) and the human ␤2 subunit (hKCNMB2). Once inactivation is removed, we find that hKCNMB2 has properties similar to mKCNMB1. hKCNMB2 slows Hslo1 channel gating and shifts the current-voltage relationship to more negative potentials. hKCNMB3 and hKCNMB4 have distinct effects on slo currents not observed with mKCNMB1 and hKCNMB2. Although we found that hKCNMB3 does interact with Hslo channels, its effects on Hslo1 channel properties were slight, increasing Hslo1 activation rates. In contrast, hKCNMB4 slows Hslo1 gating kinetics, and modulates the apparent calcium sensitivity of Hslo1. We found that the different effects of the ␤ subunits on some Hslo1 channel properties are calcium-dependent. mKCNMB1 and hKCNMB2 slow activation at 1 M but not at 10 M free calcium concentrations. hKC-NMB4 decreases Hslo1 channel openings at low calcium concentrations but increases channel openings at high calcium concentrations. These results suggest that ␤ subunits in diverse tissue types fine-tune slo channel properties to the needs of a particular cell.The large conductance calcium-activated potassium channel (BK) 1 is a unique member of the six transmembrane domain potassium channel family that is activated by voltage and calcium. BK channels are composed of a pore-forming ␣ subunit (1, 2) and, in some tissues, are tightly associated with an accessory ␤ subunit (3, 4). BK channels have diverse physiological properties with tissue-specific distribution. In neurons, BK channels are functionally colocalized with calcium channels (5, 6), shape action potential wave forms (7,8), and modulate neurotransmitter release (9, 10). In smooth muscle, BK channels regulate constriction in arteries (11), uterine contraction (12), and filtration rate in the kidney (13). Unlike other potassium channel families, BK channels can as yet only be attributed to a single gene, slowpoke (slo), that encodes the poreforming ␣ subunit of the channel. In light of the broad tissue localization and diverse functional properties, it is not surprising that a number of mechanisms have been identified that alter slo channel properties. These include alternative splicing of the slo RNA (14 -18), heteromeric assembly with other subunits (slak) (19), and modification by phosphorylation/dephosphorylation (20 -22) and oxidation/reduction (23).In addition, accessory ␤ subunits are a means of generating BK channel diversity. Coexpression of the ␤1 subunit in Xenopus oocytes increases the apparent calcium sensitivity, slows activation kinetics, and increases charybdotoxin binding affinity (24 -27). ␤1 subunit mRNA is enriched in smooth muscle (28) and can account for the apparent increased calcium sensitivity of BK channels in that tissue relative to skeletal muscl...

Synaptic inhibition within the hippocampus dentate gyrus serves a 'low-pass filtering' function that protects against hyperexcitability that leads to temporal lobe seizures. Here we demonstrate that calcium-activated potassium (BK) channel accessory beta4 subunits serve as key regulators of intrinsic firing properties that contribute to the low-pass filtering function of dentate granule cells. Notably, a critical beta4 subunit function is to preclude BK channels from contributing to membrane repolarization and thereby broaden action potentials. Longer-duration action potentials secondarily recruit SK channels, leading to greater spike frequency adaptation and reduced firing rates. In contrast, granule cells from beta4 knockout mice show a gain-of-function for BK channels that sharpens action potentials and supports higher firing rates. Consistent with breakdown of the dentate filter, beta4 knockouts show distinctive seizures emanating from the temporal cortex, demonstrating a unique nonsynaptic mechanism for gate control of hippocampal synchronization leading to temporal lobe epilepsy.

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Complementary DNAs were isolated and used to deduce the primary structures of the alpha 1 and alpha 2 subunits of the dihydropyridine-sensitive, voltage-dependent calcium channel from rabbit skeletal muscle. The alpha 1 subunit, which contains putative binding sites for calcium antagonists, is a hydrophobic protein with a sequence that is consistent with multiple transmembrane domains and shows structural and sequence homology with other voltage-dependent ion channels. In contrast, the alpha 2 subunit is a hydrophilic protein without homology to other known protein sequences. Nucleic acid hybridization studies suggest that the alpha 1 and alpha 2 subunit mRNAs are expressed differentially in a tissue-specific manner and that there is a family of genes encoding additional calcium channel subtypes.

Basal body replication during estrogen-driven ciliogenesis in the rhesus monkey (Macaca mulatta) oviduct has been studied by stereomicroscopy, rotation photography, and serial section analysis. Two pathways for basal body production are described: acentriolar basal body formation (major pathway) where procentrioles are generated from a spherical aggregate of fibers; and centriolar basal body formation, where procentrioles are generated by the diplosomal centrioles. In both pathways, the first step in procentriole formation is the arrangement of a fibrous granule precursor into an annulus. A cartwheel structure, present within the lumen of the annulus, is composed of a central cylinder with a core, spoke components, and anchor filaments. Tubule formation consists of an initiation and a growth phase. The A tubule of each triplet set first forms within the wall material of the annulus in juxtaposition to a spoke of the cartwheel. After all nine A tubules are initiated, B and C tubules begin to form. The initiation of all three tubules occurs sequentially around the procentriole. Simultaneous with tubule initiation is a nonsequential growth of each tubule. The tubules lengthen and the procentriole is complete when it is about 200 mµ long. The procentriole increases in length and diameter during its maturation into a basal body. The addition of a basal foot, nine alar sheets, and a rootlet completes the maturation process. Fibrous granules are also closely associated with the formation of these basal body accessory structures.

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The large‐conductance calcium‐activated potassium (BK) channel plays an important role in controlling membrane potential and contractility of urinary bladder smooth muscle (UBSM). These channels are composed of a pore‐forming α‐subunit and an accessory, smooth muscle‐specific, β1‐subunit. Our aim was to determine the functional role of the β1‐subunit of the BK channel in controlling the contractions of UBSM by using BK channel β1‐subunit ‘knock‐out’ (KO) mice. The β‐galactosidase reporter (lacZ gene) was targeted to the β1 locus, which provided the opportunity to examine the expression of the β1‐subunit in UBSM. Based on this approach, the β1‐subunit is highly expressed in UBSM. BK channels lacking β1‐subunits have reduced activity, consistent with a shift in BK channel voltage/Ca2+ sensitivity. Iberiotoxin, an inhibitor of BK channels, increased the amplitude and decreased the frequency of phasic contractions of UBSM strips from control mice. The effects of the β1‐subunit deletion on contractions were similar to the effect of iberiotoxin on control mice. The UBSM strips from β1‐subunit KO mice had elevated phasic contraction amplitude and decreased frequency when compared to control UBSM strips. Iberiotoxin increased the amplitude and frequency of phasic contractions, and UBSM tone of UBSM strips from β1‐subunit KO mice, suggesting that BK channels still regulate contractions in the absence of the β1‐subunit. The results indicate that the β1‐subunit, by modulating BK channel activity, plays a significant role in the regulation of phasic contractions of the urinary bladder.