Mitotic blockage following laser micro-irradiation of prosphase chromosomes

An argon laser microbeam was used to irradiate prophase chromosomes of the salamander () and the established cell of the rat kangaroo (PTK1, ). In both cell types mitosis was significantly blocked when irradiation occurred in early prophase regardless of whether or not the irradiated chromosomes were nucleola-associated. It was also determined that with identical irradiation conditions, the salamander cells were more susceptible to mitotic inhibition than the kangaroo cells. The results are compared with earlier studies performed with lower energy densities.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34174/1/0000463.pd

Argon laser micro-irradiation of mitochondria in rat myocardial cells in tissue culture : III. Irradiation of multicellular groups

Single mitochondria of contracting myocardial cells were irradiated with an argon laser microbeam and the contractility changes of the cells were noted. Four series of irradiation experiments were conducted: (i) one cell of a two-cell group was killed, (ii) one cell of a multicell group was killed, (iii) one cell of a two-cell group was damaged, (iv) one cell of a multicell group was damaged. In series (i) and (ii) a majority of cells first fibrillated and then either returned to rhythmic contraction rate, or stopped contracting. In series (iii) and (iv) the individual contractility pattern following irradiation was quite variable, but by 30 min post irradiation a majority of the cells had returned to a rhythmic contraction rate. These studies demonstrate the feasibility of using the laser microbeam to investigate cell-cell interactions, and factors involved in regulating myocardial cell contractility.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34060/1/0000338.pd

Argon laser micro-irradiation of mitochondria in rat myocardial cells in tissue culture : II. Correlation of morphology and function in irradiated single cells

It has been established that mitochondrial lesions of specific severity and morphology could be produced in myocardial cells by laser micro-beam irradiation. This paper (i) describes four general categories of contractility responses resulting from irradiation of a single mitochondrion in a beating myocardial cell (group I, no change; group II, change followed by return to rhythmic contractions; group III, cessation of contraction; group IV, cell death); (ii) correlates mitochondrial lesion type with functional response; and (iii) distinguishes between physiological deprivation of mitochondria within the cell and secondary effects due to laser energy dissipation. Of the 22 contracting cells that were altered but did not die (groups II and III) 18 returned to rhythmic contractility statistically similar to the pre-irradiation contraction rate. A definite correlation between lesion severity and functional response was noted: only cells in Group I (no change) had the least severe lesion type (8/14), and none had the most severe lesion type. Twenty of 22 cells in groups II and III had moderate type lesions, and of the 20 cells in group IV (cell death), 18 had the most severe lesion type. The short term physiological effects upon cell contractility (up to 30 minutes post-irradiation) of selective mitochondrial deletion were determined. Up to 36 large mitochondria were destroyed with the least severe lesion type, and no change in cell contractility was observed. This contrasts with the rapid cell death often obtained by destroying a single mitochondrion with the severe lesion type. The morphology and laser effects precipitating cell death are discussed. Quiescent cells have been stimulated to contract by irradiation and a few have continued to contract up to 5 minutes post-irradiation. These results are discussed in terms of the "pacemaker" cell theory.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34164/1/0000452.pd

Are chromosome secondary constrictions nucleolar organizers? : A re-examination using a laser microbeam

An argon laser microbeam was used to irradiate regions outside and inside the secondary constrictions of nucleolar organizing chromosomes. Irradiation immediately adjacent to the constriction consistently resulted in the loss of nucleolar organizing capacity. Irradiation 2 [mu]m down the chromosome from the secondary constriction did not affect the capacity to organize a nucleolus. Irradiation directly inside the secondary constriction did not affect the ability to organize a nucleolus in 50% of the cases. These data are discussed in relation to current ideas that secondary constrictions are nucleolus organizers. Alternative models are presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33537/1/0000036.pd