In the vertebrate retina, photoreceptors make synaptic contacts with two kinds of second-order neurones, bipolar and horizontal cells. The photoreceptors and horizontal cells respond to light with a sustained hyperpolarization, while bipolar cells (in this article only the depolarizing type will be considered) are depolarized. When the chemical transmission was blocked by an application of Ca++-antagonists, horizontal cells were hyperpolarized (to EK) and bipolar cells were depolarized, both to the level produced by a strong illumination. In a Na+-free medium, both types of cells were hyperpolarized. It is inferred from these observation that the transmitter from photoreceptors is continuously released in the dark and the release stops by illumination. It is further suggested that the transmitter substance depolarizes horizontal cells by increasing gNa, and hyperpolarizes bipolar cells by decreasing gNa.
This article reviews the clinical symptoms and the molecular causes of several skin diseases (dermatoses). These dermatoses are; Xeroderma Pigmentosum, Ataxia Telangiectasia, Fanconi's Syndrome, Ehlers-Danlos Syndrome and Epidermolysis Bullosa; all of them are rare hereditary diseases. Xeroderma Pigmentosum, Ataxia Telangiectasia and Fanconi's Syndrome are all clinically characterized by typical skin symptoms and high susceptivity to malignancies (skin cancer, leukemia, lympho-reticular malignancies, etc.). The nature underlying these diseases is basically thought to be due to their inability to repair DNA damage caused by some agents. Ehlers-Danlos Syndrome is a very famous connective tissue disorder, and found to be primarily due of some enzymatic defects in collagen synthetic pathway. Epidermolysis Bullosa is clinically characterized by spontaneous bulla formation on the skin. The pathogenesis is not well elucidated in molecular term at present, however, studies with this disease will help us to understand structures and functions of the skin, especially junctional part of the dermis and epidermis, as well as the epitherial tissues.
A new method was developed for the visualization of the intracellular development of phage lambda. By this new method, the presence of a complex consisting of precursor head and long DNA molecule (concatemer) can be clealy demonstrated in the host cells after infection of wild type phage. Observations of various mutants defective for head morphogenesis show that several head-related structures (empty precursor heads, head partially filled with DNA, and monsters) are present in the complex with DNA. The present investigation supports the continuous packaging of DNA into precursor heads proposed by Emmons (1974).