The complete amino-acid sequence of the receptor for dihydropyridine calcium channel blockers from rabbit skeletal muscle is predicted by cloning and sequence analysis of DNA complementary to its messenger RNA. Structural and sequence similarities to the voltage-dependent sodium channel suggest that in the transverse tubule membrane of skeletal muscle the dihydropyridine receptor may act both as voltage sensor in excitation-contraction coupling and as a calcium channel.

In cardiac muscle, where Ca2+ influx across the sarcolemma is essential for contraction, the dihydropyridine (DHP)-sensitive L-type calcium channel represents the major entry pathway of extracellular Ca2+. We have previously elucidated the primary structure of the rabbit skeletal muscle DHP receptor by cloning and sequencing the complementary DNA. An expression plasmid carrying this cDNA, microinjected into cultured skeletal muscle cells from mice with muscular dysgenesis, has been shown to restore both excitation-contraction coupling and slow calcium current missing from these cells, so that a dual role for the DHP receptor in skeletal muscle transverse tubules is suggested. We report here the complete amino-acid sequence of the rabbit cardiac DHP receptor, deduced from the cDNA sequence. We also show that messenger RNA derived from the cardiac DHP receptor cDNA is sufficient to direct the formation of a functional DHP-sensitive calcium channel in Xenopus oocytes. Furthermore, higher calcium-channel activity is observed when mRNA specific for the polypeptide of relative molecular mass approximately 140,000 (alpha 2-subunit) associated with skeletal muscle DHP receptor is co-injected.

The primary structure of a voltage-dependent calcium channel from rabbit brain has been deduced by cloning and sequencing the complementary DNA. Calcium channel activity expressed from the cDNA is dramatically increased by coexpression of the alpha 2 and beta subunits, known to be associated with the dihydropyridine receptor. This channel is a high voltage-activated calcium channel that is insensitive both to nifedipine and to omega-conotoxin. We suggest that it is expressed predominantly in cerebellar Purkinje cells and granule cells.

Physiological experiments have produced evidence that the middle temporal visual area (MT) of the monkey is selectively involved in the analysis of visual motion. We tested this hypothesis by studying the effects of small chemical lesions of MT on eye movements made in response to moving as opposed to stationary visual targets. We observed two deficits for eye movements made to moving targets: a monkey's ability to match the speed of his smooth pursuit eye movements to the speed of the moving target was impaired, and a monkey's ability to adjust the amplitude of a saccadic eye movement to compensate for target motion was impaired. In contrast, saccades to stationary targets were unaffected by the MT lesions, suggesting that monkeys with MT lesions had more difficulty responding to moving than to stationary stimuli. These results provide the first behavioral evidence that neural processing in MT contributes to the cortical analysis of visual motion.Primate extrastriate visual cortex is composed of a remarkable array of distinct visual areas. In the macaque monkey no fewer than nine extrastriate areas have been identified on the basis of anatomical connections, visual topography, cortical architectonics, and single neuron response properties (for reviews, see Zeki, 1978;Van Essen, 1979; Woolsey, 1981). How these areas individually and collectively contribute to vision is a central issue for a neurobiological understanding of visual processing.Perhaps the most intensively studied of these areas is the middle temporal visual area (MT), an area in the posterior bank of the superior temporal sulcus (STS) which receives a direct projection

Cloning and sequence analysis of DNA complementary to porcine cerebral messenger RNA encoding the muscarinic acetylcholine receptor predict the complete amino-acid sequence of this protein. Expression of the complementary DNA produced functional muscarinic receptor in Xenopus oocytes. The muscarinic receptor is homologous with the beta-adrenergic receptor and rhodopsin in both amino-acid sequence and suggested transmembrane topography.

The skeletal muscle dihydropyridine (DHP) receptor is essential in excitation-contraction (EC) coupling. The receptor is postulated to be the voltage sensor giving rise to the intramembrane current, termed charge movement. We have now tested this hypothesis using myotubes from mice with the muscular dysgenesis mutation, which alters the skeletal muscle DHP receptor gene and prevents its expression. Our results indicate that charge movement is deficient in dysgenic myotubes but is fully restored following injection of an expression plasmid carrying the rabbit skeletal muscle DHP receptor complementary DNA, strongly supporting the hypothesis that the DHP receptor is the voltage sensor for EC coupling in skeletal muscle. Additionally, our data obtained for normal and chimaeric DHP receptor constructs demonstrate that DHP receptors with widely differing abilities to function as calcium channels and to mediate EC coupling produce very similar charge movements.

Mechanisms of direction selectivity and speed selectivity were studied in single neurons of the middle temporal visual area (MT) of behaving macaque monkeys. Visual stimuli were presented in both smooth and stroboscopic motion within a neuron's receptive field as the monkey fixated a stationary point of light. Direction selectivity, speed selectivity, and the spontaneous discharge characteristics of MT neurons in behaving monkeys were similar to those reported in previous studies in anesthetized monkeys. Stroboscopic motion stimuli were sequences of flashes characterized by the spatial and temporal intervals between each flash. The spatial and temporal intervals were systematically varied so that suppressive and facilitatory interactions could be studied in both the preferred and null directions. Suppression and facilitation were measured by subtracting the peak discharge rate elicited by a single flash from the peak discharge rate elicited by a stroboscopic train of flashes. The dominant mechanism of direction selectivity in MT was a pronounced suppression of discharge for motion in the null direction which we interpreted as inhibition. The inhibition was sufficiently potent to abolish the responses to single flashed stimuli when they were embedded in a series of flashes in the null direction, and it frequently reduced the neuronal discharge to a level below the spontaneous firing rate. Facilitation in the preferred direction was a prominent feature of the responses of some, but not all, MT neurons. The peak discharge rate for stroboscopic motion in the preferred direction was more than twice the peak rate to a single flash for approximately 50% of the neurons in our sample. The direction selectivity of most MT neurons showed the effects of both inhibitory and facilitatory mechanisms, and it was not possible to segregate MT neurons into distinct groups on the basis of these measures. Suppressive mechanisms contributed to speed tuning as well as direction tuning. The low-speed cutoff for motion in the preferred direction resulted from suppression in 82% of the neurons tested. The high-speed cutoff resulted from suppression in 32% of the neurons tested. The latter mechanism appeared to be distinct from the inhibitory mechanism which acted in the null direction in that large spatial intervals were required for its activation.

We present evidence that vimentin intermediate filament (IF) motility in vivo is associated with cytoplasmic dynein. Immunofluorescence reveals that subunits of dynein and dynactin are associated with all structural forms of vimentin in baby hamster kidney-21 cells. This relationship is also supported by the presence of numerous components of dynein and dynactin in IF-enriched cytoskeletal preparations. Overexpression of dynamitin biases IF motility toward the cell surface, leading to a perinuclear clearance of IFs and their redistribution to the cell surface. IF-enriched cytoskeletal preparations from dynamitin-overexpressing cells contain decreased amounts of dynein, actin-related protein-1, and p150Glued relative to controls. In contrast, the amount of dynamitin is unaltered in these preparations, indicating that it is involved in linking vimentin cargo to dynactin. The results demonstrate that dynein and dynactin are required for the normal organization of vimentin IF networks in vivo. These results together with those of previous studies also suggest that a balance among the microtubule (MT) minus and plus end–directed motors, cytoplasmic dynein, and kinesin are required for the assembly and maintenance of type III IF networks in interphase cells. Furthermore, these motors are to a large extent responsible for the long recognized relationships between vimentin IFs and MTs.